if you want to buy then i recommend
www.theoverclockingstore.co.uk
www.overclockedpc.co.uk but they are offline at the moment
www.extremecooling.co.uk
if you want to diy then go to a vauxhall scrap yard and ask for a copper nova heater core or cavalier heater core.
nova core
cav core
both of these will fit in the front of a cheiftec case if you remove the lower hard drives.
if you have any good aquarium stores near buy you should be able to pickup a good pump. also garden centers might be good too. The overclocking store do good prices on the ehiem 1048 and 1250 pumps.
www.rswww.com are good for barbs and most fittings.
i agree about getting kits go for a good custom rig with 3/8 or 1/2 silicon tube , ehiem pump and a copper heater core. I made the mistake of getting a koolance exos and my home made rig takes 4C of the temps. Now i am struggeling to sell it.
As for a water block i cant comment as i made my own but depending on your budget go for the best which at the moment is the white water when you can get one in the uk.
otherwise a maze 3 is a good choice for a start.
hope this helps
Lee