Wow, a whole new forum category...
Well, as far as clutches go, there are a few things to consider. The first thing which limits what clutches you will be looking at is the holding capacity. This is how much torque the clutch can stand without slipping. This of course will be dependant on your car and also how much it has been (will be) tuned.
There are 3 main parts to a clutch. The pressure plate, the flywheel and in between the two is the clutch disc or friction disc. The design of the pressure plate and the springs on the pressure plate will determine how much pressure it can apply to force the clutch disc to the flywheel. This also generally determines how 'heavy' the clutch pedal feels. Generally the greater the capacity of the pressure plate, the heavier the pedal will feel. There are designs which change the leverage from the stock setup, which allow a stronger clutch to feel the same as the stock clutch though.
As for the clutch disc, there are many types, but they basically divide into sprung hub and solid hub discs. Sprung hub discs have coil springs between the hub and disc to absorb the shock of engagement when the clutch first starts to 'catch'. Solid hub discs have no springs. They are usually used only in very high torque situations where a sprung hub might not be able to cope with the load. There are also different kinds of friction materials, ranging from organic (most stock clutches) to kevlar, bronze metallic, sintered iron and carbon. They all have different characteristics, differing in how much friction they have and how aggressively they engage, and also how durable they are. It would be quite an essay to review the differences in these materials and how they perform under various conditions, but here's a link that has a lot of basic info. Note that since this particular company doesn't make carbon clutches, they don't have any info on those
http://www.ramclutches.com/Clutch%20...university.htm
BTW, this isn't an endorsement for their clutches. I've heard some decent things about their clutches, but have no personal experience with them. The link has decent info on clutches in general though. As for my VR-4, I've got a single plate carbon-carbon clutch in it by RPS. Holding capacity of 600ft-lbs. Since I'm not predominantly a drag racer, this clutch works out nicely for me. They have a twin disc carbon-carbon good for 1000+ft-lbs.