What you can get onto the SSD depends on the size. If it is a 30-40GB drive then it would be the OS and one or two large-ish programs. If it is a 60-80GB drive then you could get the OS plus quite a few programs, and probably a few games. ~120GB would house all programs and lots of games.
Seeing as you have a Z68 chipset motherboard you also have the option of using your SSD as a cache to store the most commonly used programs to help speed them up.
OCZ Vertex 2 40GB £62
http://www.ebuyer.com/232639-ocz-vertex-2-series-40gb-sata-ii-2-5-ssd-oczssd2-2vtx40g
There are a few websites like this:
http://www.pcspecialist.co.uk/
Which allow you to customise a build to your liking, but I'm not convinced you will find one of those sites which will be able to match the price/quality of a self build. Plus it is pretty easy to build one yourself, so I'd recommend you do that.