I just bought a Trek 8000 which has Avid SD3 Calipers & Shimano LX levers. They work pretty good, but I do feel like there is room for improvement in the breaking system on my bike.
I plan on upgrading to discs but like everyone else said I'm going to wait a year or two. Not only will disc breaks get cheeper, better and lighter, but so will tubeless wheel systems. If I have to replace my wheels I'm definatly going to go tubeless at the same time. If I had the money I'd get the CrossMax UST Disc today, but at almost 900$ I'll think I'll wait for technology to get better and get a pair of 2003 CrossRocs or whatever.