Just read these stats about the top 10 Facebook games as of June 9th:
1: Friends For Sale! (633,897 active players)
2: TexasHoldEmPoker (553,999)
3: Scrabulous (444,548)
4: (Lil) Green Patch (437, 847)
5: Mob Wars (288, 372)
6: Who Has The Biggest Brain? (279,242)
7: Speed Racing (207, 283)
8: Bowling Buddies (205, 716)
9: Pokey! (202,161)
10: Word Challenge (193, 850)
That’s pretty impressive. I haven’t actually tried any of these because Facebook is EVIL (well, actually it’s just a waste of my precious time, so I don’t bother). I assume these games generate revenue from adverts (I could be wrong) in which case they should be doing pretty well.
Another approach would be to link to download games (or ad-driven online games) on your own site so that users might play the Facebook game and then end up on your site (great for generating traffic especially as some Facebook games generate MILLIONS of unique visitors per month).