So many to choose from! Off the top of my head, three UX folks who I enjoy the writings of (and hence follow on Twitter) are Patrick Neeman ([@usabilitycounts), Whitney Hess ([URL="https://twitter.com/whitneyhess"]@whitneyhess) and Bret Victor (@worrydream(https://twitter.com/usabilitycounts)). I don't know if Bret Victor counts as a "UX guy". He's more of a genius design/code/thinking triple act who has come up with some incredible stuff.
I kind of dip in and out of Twitter—a bit like talkback radio. I miss a lot of stuff that flies on past, but I'm not worried about that and don't try and keep up.