Jim pretty much covered it all, but I would stress that if you can, you really should get the 6800GT. The 6600 offers no real performance benefit over a 9700 (in terms of AA, AF and the like). Case is really up to yourself, I like my Akasa Exlipse 62, but it cost me a fair bit more than that one, and came without a PSU. Advantages are, it's extremely roomy, and has great cooling (through 2 120mm fans). I would also stress the fact that you should look at a quality PSU. The Tagan 480W for example, will last you years, and is a great investment.
The Asus A8N SLi Deluxe is a great board, I own one myself and am exteremly happy with it. If you could afford it, it might be worth spending about £150 on RAM (RAM is *extremely* cheap at the moment, and rumoured to be going on the up soon) and then buy a 3000 venice/winchester, and overclock it. Obviously its up to personal choice on whether you wish to overclock.
If it was me, I'd stay away from the bundles, as there's none there I would say were spectacular.
Also, Overclockers does have a bad reputation for returns, but I'm with you, I love them. There site layout is by far the best/simplest/easiest to work with among the competition, and they delivery promptly too. Although I've never had to return goods with them. If you did want to look elsewhere (although you mentioned you liked them) then
www.scan.co.uk is a reputable and good source, where I've purchased thousands of pounds worth of stuff without a problem.
Good luck,
Ross