The big thing lately has been the eggbeaters by Crank Brothers. These resemble a four sided cage that allows mud/water/etc. to fall through, helping to keep the system from clogging. They can be found for under $50 now at most any mail-order site (unless you weant the titanium version=$$$$). Time Atacs are a favorite, with a wide platform. This is especially helpful if this is your first pair in a while. Shimano 959's are also popular. I currently run my first set of clipless that I owned, Shimano 536's, on my XC bike and they have worked well. They have a relatively wide platform around the mechanism which helped when I was learning. The mud clearance doesn't seem too bad - sometimes it takes a try or two, but they always clear out and work. My next pair will either be a set of Atacs or the eggbeaters - haven't decided yet. Check out
www.mtbr.com for more reviews on different pedals that you find.
-Moab