Hi Sean,
The basic choice is between self-inflating mats (SIMs), closed cell foam mats (aka 'rollmats' or 'karrimats') or a combination of the two, and air-mats (a bit like a hi-tech Lilo - the NeoAir is one of the best known). There is also Thermarest's Z-lite folding mat to consider.
I've not had any first-hand experience of air-mats but no doubt other OM-ers can give you chapter and verse on them.
The main advantage of CCF mats ('rollmats') is light weight and low cost. They are also water-resistant in that the closed cell foam doesn't absorb water - if it gets wet, just wipe it dry - so you can carry them outside your pack. Another plus point is that, unlike a SIM or air-mat, you can't puncture a rollmat. The main drawbacks are that rollmats give little cushioning and, if carried as a roll, can be awkwardly bulky.
IME, you will sleep comfortably (and, probably, warmly) on a SIM. The main advantage of a SIM (and also of an air-mat) is comparitively good cushioning - that's particularly important if you sleep on your side. SIMs also provide very good insulation from ground chill (though air-mats are less effective insulators).
A sleeping system is a very personal thing. Everyone has their own preferences. I sleep very comfortably on a SIM (although I can't get on with three-quarter length where one's legs hang off the end.
I use a full-length Mountain Equipment Helium 3.8 and I've had no problems with it so far. (I also have an Alpkit Wedge for car-camping but it's much too bulky for backpacking).
I find the combination of the SIM and a down sleeping bag warm enough for most temperatures but when it gets near freezing I also carry a cut-down rollmat to provide additional insulation.
Therm-A-Rest is one of the best-known manufacturers of SIMs and air-mats but there are plenty of other makes. Nearer home, for example, you might consider the Alpkit range. And here's the link to Exped .
For more possibilities type 'camping +sleeping mats' into Google.
(All the above IMHO, of course)
Edited: 04/05/2012 at 08:27