Sticking with V's for now still havn't felt the need for disks. Just did a four day trail ride through the hills south of my town replete with horror downhills, rocky washaways and creek crossings v-brakes did fine.
I'm pretty heavy (95kg) and I ride down some pretty steep hills on my local trail. The V's have brilliant stopping power. Have only experienced discs on short rides on various friends' bikes, but given the current performance of my V-brakes I see no need to fork out extra moola on discs.
Bear in mind I'm not a racer, but on the serious side of a recreational XC rider.
I've got V brakes on both of my bikes. Deore LX on my Sugar and Avid SD-5's on my GF Cake. For my own preferances, I just havn't felt that disc brakes are that much better than V-brakes. I mean, they're nicer in the sense of less hand fatigue. But V-brakes are effective and disc brakes add weight to the bike. I like mine as light as I can get it.
Hmmmm, I think there used to be one called a U-Brake.....I think that is what is was called. It was the same concept as the V-Brake, but on the back wheel, instead of being mounted at the top of the seat stays, near the seat post, it was mounted to the chain stays down by the front derailer. It was weird, my dad's old, old, Mt. Bike has one. I don't think that they do that anymore cause' it collected so much mud. But other than that, I don't know of any other break types.
Ther are hydraulic rim brakes such as the old maguras. The older style cantilever brakes which used to be used on mountain bikes and are still used in cyclocross, coaster brakes, there are even some weird hub brakes, etc.
I've never ridden V's, I road many different cantilevers, and my next bike had hayes discs. I've had these breaks for 3 years and I've never even changed a pad. I've never gone a day with no breaks, can't say the same about my cantilever days. I'd never go with rim breaks again. The power of a hydraulic disc break is just unbeatable. What does a motor cycle use? Or your car for that matter. It is simply the best way to stop a moving object outside of artificial gravity fields :-D
Hayes hydraulic discs; HFX-Mag on the front, HFX-9 on the rear.
If I were to do it all over again, I'd get HFX-Mags for the rear too (I only got the 9's because I needed to buy just one end, and the 9s were quite a bit cheaper at the time.) The feel of the brakes is just that bit nicer.