For me:
Vibram Fivefingers - short easy runs, recovery runs, cross-training. Surprised at how much I enjoy the occasional easy run or gym session in these.
Saucony Fastwitch 5 - speedwork, shorter tempos, road races 5k-half marathon, triathlon racing. Versatile shoe, love it.
Saucony Kinvara 3 - long tempos, fartleks, races HM-marathon. A bit softer than the fastwitch but still responsive and good for slightly faster running.
Asics Gel-Neo33 - base mileage. This is a comfortable, cushioned, somewhat supportive shoe that I just throw on for cranking out the maintenance miles.