It depends on the type of music that you want to play with it I guess. If you want a good wah for metal check out the DIME Crybaby From Hell or the Zakk Wylde Crybaby. I have a ZWCB and it screams. They're basically Jimi Hendrix wahs that are slightly modified with a few gizmos to give it a ton more edge. On that note, the Jimi Hendrix Wah from Dunlop would be great for mellow stuff. The Morley wahs look pretty sweet... I almost bought a Tremonti... but I opted for the ZW. I haven't really played them other than a few times in stores. A couple other ones that I've wanted to check out are the Ibanez Weeping Demon, the DigiTech Wammy, and the DigiTech Jimi Hendrix Experience Wah. Those are just some suggestions for ya. So here's a breakdown:

Metal/Hardrock: Tremonti Wah, Zakk Wylde, Crybaby From Hell, Bad Horsie
Alternative: Crybaby, Tremonti, Bad Horsie
Blues: Digitech Hendrix Experience, Jimi Hendrix, Bad Horsie