I have just bought a bike. I'm very happy because that completes my fleet**.
Bike A) Road fixie - For commuting and generally getting from A to B
Bike B) Good old slick tired MTB - Used as a hybrid for commuting when I'm feeling under the weather, getting the shopping, towing trailers, riding trails and maybe even touring.
Bike C) MTB - For learning to ride rough stuff - I'm pleased I'll no longer be wearing out the knobblies and other nice componentry on the road with mundane* utility trips
Bike D) Tandem - Only really half a bike but it's a lot of fun!
*Not that cycling is ever mundane, except maybe for long stretches of A road dual carriageway
**There is also bike E. My Airborne Valkyrie Ax. Bike E is only half a bike. It exists as just a frameset right now. It was the best bike I ever had. I will build it up again one day, when finances allow and we are living somewhere it's less likely to get nicked. Meanwhile, it bides it's time.