My road bikes see more crappy weather than my mountain bikes, due to the fragility of our local trails when wet.

I don't do ice, severe storms (as NYbiker mentioned), or high winds. Pouring rain stinks from visibility and sogginess standpoints, but I've done it... My biggest turn-off about riding in the rain is all of the bike cleaning that happens afterwards.

As far as rain gear, I aim for staying warm rather than dry, especially during the summer. A vest, some lightweight full-finger gloves, lightweight wool socks, clear glasses, and a cycling cap with brim are my must-haves. After that, it really depends on the specific conditions and whether or not I add more layers.