I am a pack rat and a collector of game books. It doesn't even matter what system they're from. If I see something I like in them, I'll buy them. Thus, I have a gaming library that is full of all sorts of adventures and sourcebooks from different game systems. As I peruse them from time to time, I get to thinking about how I could use adventures from one system in another. Since many of my books are old D&D stuff, those wind up getting a lot of thought in this department. So in this post, I'm going to discuss some of the adventures I think could be translated into a Star Wars setting.
This series is one of the easiest translations in my opinion. The slavers would be raiding planets instead of coastlines, and each of their bases could be on a different world. The temple in Highport (Module A1) could be a remote 'pirate' type port on the Outer Rim. From there, you would learn the location of the Hill Fort (Module A2)—perhaps an old ruin on another planet. And finally, you could follow the trail to a seemingly barren and volcanic world which houses the 'Aerie' of the Slave lords (Modules A3-4) in a sheltered (domed?) valley. Since all these modules are relatively low-magic, you wouldn't have to change a whole lot. Even the various creatures can be explained away as Alien races or monsters (the Aspis Insect-Men, for instance). Markessa (from A2) could be a genetic scientist (thus explaining her bizarre and warped creations). As far as the Slave Lords themselves go, the mages and clerics among them could easily translate into minor Force Users (rogue sith, dark force 'mages', etc.). Since each of these adventures involves infiltration and (in most cases) rescue of slaves, it is an easy matter to avoid the 'nuke it from orbit' solution that can pop up with many Fantasy-to-Sci-Fi conversions.
Against the Giants
This one is a bit more tricky to handle than the Slave Lords. The setting is easy enough: Picture the remote agricultural world of Sterich. After defeating the native gigantic humanoid races of the planet, the settlers suddenly find themselves under concerted assault by highly organized bands of the brutes. The characters would be hired to come in and put an end to the assault (and find out who's behind it). It is...a bit more difficult in this adventure to avoid the use of starships and bombardment. The Steading of the Hill Giants (G1) could easily be strafed by your average PC ship—unless you give the Giants access to some anti-air weapons (supplied by their mysterious organizers?). The Glacial Rift (G2) and Halls (G3) would be more secure from Air assault, however, requiring players to go in on foot. But then, this all brings up the question of just HOW can characters battle giant humanoids. First of all, they could bring heavy weaponry (rocket launchers and heavy repeating blasters). Or, more interestingly, they could be supplied with a small amount of power-armor or even combat walkers. This is going to change the dynamics of the adventure considerably, but could still be kind of cool.
Descent into the Depths
Whether or not you get ambitious enough to convert the Giants adventure, the Descent series could still work. With the Giants, you find out that an evil, underground race is actually supplying them with arms and provoking the attacks. Without the Giants, perhaps local settlers in a remote system have suddenly disappeared or been attacked by unknown foes at night. In either case, the trail leads the characters deep underground, through the lairs of fierce cave-dwelling species and monsters. The adventure would culminate in the foul and degenerate lair of the Drow—whom I see as an entire race of force-sensitive and force-using evil near-humans who worship a force-warped and seemingly 'immortal goddess' Lolth—who could be a Force Spirit or simply a very ancient force user kept alive by draining others life force (or even ancient cloning technology). Including the 'Demonweb Pits' (with their extra-dimensional-gateway aspect) in all of this would be a bit more fantastic than my own tastes, though you COULD include the giant Spider-Ship thing if you wanted—Lolth's Creation that she intends to use to move to another world (or something).
Dwellers of the Forbidden City
This would make a fun adventure for an exploration-geared party—following rumors to a lost city in the midst of a thick jungle. Again, you'd have to find some way to rein in the use of Starships, otherwise, it could easily degenerate into a situation where the party simply strafes the locations of the bad guys then goes in to sift through the rubble. My suggestion to deal with this would be to have some ancient defensive mechanism still in place, either a shield or an ion thing of some sort that prevents flyovers. The remote nature of the city itself would mean the players would then have to go in on foot (and through the caverns) to reach it. Again, the monsters could easily be native species vying for control—with the Yuan-Ti being the remnants of a degenerate former race.
I've actually run this one as a Star Wars conversion, and it seemed to work just fine. Strahd the Vampire becomes Strahd the Dark Jedi. To prevent use of starships is simple enough- the castle itself is defended by a shield generator deep beneath it. Of course the fact that innocents might be held captive in the castle would also be a deterrent to liberal use of aerial firepower. I remember I had to give Strahd a few more extreme force powers, however, to make him more vampiric—thus he was 'undead' in a way, not just a pale-skinned sith.
Tomb of Horrors
I haven't really looked to closely as to how this would translate—but it intrigues me nonetheless. Many of the deadly traps herein could be explained by various types of high-technology gizmos—perhaps even 'lost' technology from some ancient race. Of course the 'killer' tone of the module would (in my campaign at least) have to be cranked down a few notches—leaving it challenging, but not total-party-killing. The demi-lich himself would be difficult to handle, he could be a 'dark Jedi' or some such, but that may be too much cliche (considering a lot of the other 'magical' elements in adventures are easily force related). Perhaps the demi-lich in this is actually the mind of an ancient 'mad-inventor', now living in a computer system that monitors and controls the deadly traps in the tomb.
White Plume Mountain
I see this adventure much in the same vein as the Tomb of Horrors. A 'funhouse' of traps and the like accomplished through technology rather than magic. The monsters living within could even be cryogenically preserved and activated only when sensors detect the party entering. As far as the over-riding plot of the adventure (recovering the three weapon-artifacts) perhaps they're ancient Jedi/Sith heirlooms? Heh...Imagine a 'Blackrazor'-esque lightsaber. Booyah.
Expedition to the Barrier Peaks
Since it's about exploring a crashed alien ship, the translation of this adventure would be relatively easy to accomplish. In a Star Wars setting, however, it would become a lot more 'routine' than in its original form, as the whole aspect of learning how to use technological devices would be lost.
The overall plot of the 'U' series modules is an interesting one. Consider a remote swamp planet with a small modern settlement (Saltmarsh). The locals notice strange goings on around an old (and supposedly haunted) ruins. The PCs are hired to check it out and discover a smuggling ring operating in the area (U1)—and they seem to be supplying the primitive lizard-man tribes with arms! The PCs are then sent to try to pre-empt the imminent lizard-man attack (U2), only to discover that the arms aren't intended to be used against the settlement, but rather against a hostile tribe of sea-dwelling natives seeking the destruction of the lizard-men (and eventually conquest of the settlement). In the final installment (U3), the PCs team up with a band of lizard-men and townsfolk to attack the underwater lair of the bad-guy tribe. Yep. Seems to work for me, and it could be a fun aquatic adventure—not your typical setting.
Isle of Dread
You have to look no further than the King Kong movies to see how this adventure might be converted. A lost planet populated by fierce creatures and perhaps an ancient evil race (the Kopru). Though it is a cliche in Star Wars adventures, the best way to get players onto the planet (and keep them that way) is to have them crash-land (have the planet surrounded by some strange mist and magnetic fields that play havoc with their technology). Once on the ground, the search for parts from other crashed ships would keep them moving, even into the domains of the scary beasties. I figure some the 'native' tribesmen in this case would actually be the degenerate descendants of crashed starship crews, living behind gigantic fortress walls. The 'inland' natives could be ex-slaves of the now fallen Kopru empire, etc.
So anyway, these are just a few ideas with what I see are the most adaptable modules. I'm sure there are more if you put your mind to it—and once again, it shows to me the all-inclusive nature of the setting and just how many different things it can encompass.