There are other companies on my list, but these would be the top contenders for my consumer dollars.
I'm also keeping my eye on Sovereign Press (Sovereign Stone), Troll Lord Games (Gygax books), and Atlas (Nyambe was great. I'd love to see them do other "culture" books).
1. WotC (Oriental Adventures, Call of Cthulhu, Core books, Psionics Handbook... I don't think there is a product I have purchased from them that I haven't made use of yet)
2. Malhavoc Press (Monte Cook is amazing)
3. Bad Axe Games (Crunchy character books are great, lots of useful ideas)
4. Sword & Sorcery Games (Lots of great spells and monsters and a interesting setting)
5. Fiery Dragon Press (Great adventures and counters)
1. WOTC-by default, without them we wouldn't have the others to choose from, and they put out Call of Cthulhu d20 which has allowed me to play CoC with people who are new to rpgs and only know d20
2. Fiery Dragon-Counter Collections-the counter collections have made gaming so much easier, and look better than all the unpainted miniatures that I have
3. Sword & Sorcery-Scarred Lands books are great, even if I'm not running a game there currently, I am really enjoying the world
4. Malhavoc Press-I regularly use both Books of Eldrich Might in my game
5. Green Ronin-Armies of the Abyss & Legions of Hell-great resources for demons & devils
Honorable Mention. Kenzer-I really like some of the books they have put out as resources for my game, but I doubt I will ever run in the Kalamar setting, something about it just doesn't feel right to me
Here's my list based on quality of writing/editing, artwork & layout & how much it is used in my campaign.
1) Malhavoc A lot of bang for the buck, nice 'look' & few gaffs or errors. The only product that's sitting on the shelf is Demon God's Fane which I haven't got to run (yet). BoEM I & II are considered "core" in our game.
2) WotC Overall as good as it gets from a layout & illustration standpoint (though Privateer gets close IMO). Several of the books look nice but rarely get used. Deites & Demigods and Book of Challenges were both a real waste FMC.
3) Necromancer Good layout & moody illos. Some probs w/ the early releases w/ maps & other things. Lately has gotten better & better. Hard to beat the online support. Tomb of Absythor & Demons & Devils are two of the best values available.
4) AEG Great ideas & good value in the "One Word" line. The Rokugan line is exceptional. Editing & mechanics could be stronger.
5) Privateer Press Gorgeous looking material & B&W illos far surpassing most other companies. Great ideas, intriguing campaign world & would perhaps rank higher if we could see more releases. The Monsternomicon may be the best 'Monster book' on the market. Who says you need expensive, full color illos to have a great looking book. More please.