The number of supplements for this game is somewhat daunting. Which ones would you recommend? I'm not that interested in prefab adventures and primarily aim to play during the original trilogy.

2nd Revised? The core book. Maaaaybe the Trilogy Sourcebook. 1st edition? The core book and the Star Wars Sourcebook. Seriously. If you're playing in the era of the movies (the only ones worth seeing), this covers everything you need.

2nd Edition, Revised & Expanded
Trilogy Sourcebook
Imperial Sourcebook
Rebel Alliance Sourcebook
Galaxy Guides: Tramp Freighters, Scouts, Bounty Hunters
Planets Collection
Privateers and Pirates

The above books cover everything you need and then some (you really just need the Core Rulebook and the Trilogy Sourcebook). The rest of the books are worth a look for interesting tidbits that can expand your game.

Honestly, you need fewer than you think you do.  There's considerable overlap between supplements and how many times do you need the write up for Zero-G spacetroopers?  If I had to run a game next week I'd use:

2nd Edition, Revised and Expanded
Galaxy Guide 6:  Tramp Freighters
Star Wars Sourcebook
Thrawn Trilogy Sourcebook (maybe)

Pretty much every sourcebook has neat, cool and useful information on it and I wouldn't steer you away from picking up anything you're interested in.  Back in my budget conscious teenage days there wasn't a sourcebook that I ever felt ripped off after purchase.  I certainly can't say that now with other systems.  However, these days there's the internet with sites like The Rancor's Pit and a million conversions for different systems to Star Wars, I'd say you're less dependent on sourcebooks than back in the mid 90s.

Echoing the above, I'd add that a given Adventure Journal was as good a buy as almost all 9f tye sourcebooks.  They're all mostly just fodder for ideas.

My main stays for the years that I ran WEG were:
- Star Wars 1e
- Star Wars Sourcebook
- Rebel Alliance Sourcebook
- Imperial Sourcebook

The Rebel Alliance Sourcebook was the least used of the 4.

I'm a WEG Star Wars fan myself but when talking supplements it's hard to beat the D20 Star Wars Galactic Campaign Guide in terms of sheer usefulness and versatility.

Quote from: Soylent Green;737322I'm a WEG Star Wars fan myself but when talking supplements it's hard to beat the D20 Star Wars Galactic Campaign Guide in terms of sheer usefulness and versatility.

Good call. That is the one sourcebook from the RCR edition that I have kept. I still use it when running WEG, Saga Ed or EotE

Quote from: Skywalker;737317My main stays for the years that I ran WEG were:
- Star Wars 1e
- Star Wars Sourcebook
- Rebel Alliance Sourcebook
- Imperial Sourcebook

That's my set up as well.

Plus the Rules Companion if you want more cruft.

Tales of the Jedi, if you are interested in a comprehensive list of Force powers

I like aliens and droids, and I know my players would like to play aliens and droids. Any of the books particularly useful or recommendable for that?

It's also fun to have a nice variety of ships available so that not every piraty/smugglery/bounty huntery-crew ends up in a modified YT-1300.

Quote from: Soylent Green;737322I'm a WEG Star Wars fan myself but when talking supplements it's hard to beat the D20 Star Wars Galactic Campaign Guide in terms of sheer usefulness and versatility.

Quote from: Skywalker;737324Good call. That is the one sourcebook from the RCR edition that I have kept. I still use it when running WEG, Saga Ed or EotE

Ditto.  I'm not getting any more play out of d20 Star Wars, but I am still getting a lot of value out of that book.

I think I would go with:
Rebel Alliance sourcebook
Imperial sourcebook
Galaxy Guide 6: Tramp Freighters
Galaxy Guide 9: Fragments from the Rim

The first two are excellent resources for both your good guys and baddies. The Tramp Freighter book helps make the heroes a home, and sweet ride.
GG9 is a bit slapdash, but it really helps to set the mood of the WEG Star Wars universe. It's also a gold mine of adventure possibilities, if you need something to mine from.

There's also two Fantastic Technology's books, that a lot of my players loved. I feel they're more 007 Gimmick books, but they can be useful.

I suggest the Marvel Star Wars comics. Issues 1 to 27 are collected in an Omnibus. It's vintage 70s Marvel and extrapolates the universe from only the first movie.

INFO
http://starwars.wikia.com/wiki/Omnibus:_A_Long_Time_Ago..._Volume_1

AMAZON
http://www.amazon.com/Star-Wars-Omnibus-Long-Time/dp/1595824863

Quote from: Skywalker;737317My main stays for the years that I ran WEG were:
- Star Wars 1e
- Star Wars Sourcebook
- Rebel Alliance Sourcebook
- Imperial Sourcebook

The Rebel Alliance Sourcebook was the least used of the 4.

That's basically it. I could do without the Rebel Alliance sourcebook, but the Imperial one had some really good bits.