I only have three, and one (the Trek) is probably on its way out:

Trek 1500 road bike (ca. 1990 except for frame, rear derailleur and brake levers, all of which have been replaced over the years)
Fisher Marlin mountain bike (currently running 1.5" street tires)
Cannondale Synapse Alloy 5 road bike

While I'd love a hi-zoot racing bike like a nice Pinarello or something just for the flash, it hain't gonna happen. The only N+1 I can realistically see getting sometime is a bike that's more suitable to fast city riding/commuting/errands. Maybe something from Salsa, or if I win the lottery, a Hampsten Special/Zucchera.