I'm going for 3 different complete sets: Sega Saturn, Sega CD, and NES. I've got 90 of the 255 Saturn games, 46 of the 147 Sega CD games, and 260 NES games, but I've always planned on that set taking me tens of years to complete, so I don't rush myself in that set. The Sega sets I plan on finishing within the next few years. I could have tons more, but I always hold out for nice copies, with limited to no case cracks, and of course they have to be complete, unless it's just a smoking deal like $1 or something for a good game.
I'll tell you what though, this site has been infinitely helpful in tracking my collection on the go, it's kept me from buying doubles on a number of occasions. Three cheers for vgcollect!