OcUK are good, but I always check Scan as they can sometimes be a little cheaper.
I wouldn't go for a high, high end CPU - I'd save that money and put it towards the best graphics card you can afford if it is going to be a gaming machine. Any modern Intel CPU will be fine.
A solid state drive is something to consider, but I wouldn't blow the budget on a large SSD. They're only really going to cut down loading times (are people really that impatient?) and once the data is in memory you're no longer waiting on the hard drive.
Speaking of memory, I'd go for 4GB no question as it's really cheap at the moment.
Don't spend a lot on a heatsink and fan if you don't plan to overclock. The stock fans are fine and the only reason I'd buy a third party one is they tend to be quieter.
Finally, don't skimp on the PSU and case. If you can afford the room buy a large case as they are much easier to work with.
Hope that helps.