Personally I don't think you can go much wrong with the Logitech Driving Force GT.
It roughly half the price of the G27, and it's pretty good. A would say quite lot of guys around here started with that wheel. I certainly did.
Logitech list it at £129.99 (G27 £269.00), but you can usually get it cheaper elsewhere. When I got it, it was £89.99 in Argos. I don't think they sell them anymore.
Current ebay listings :-
http://www.ebay.co.uk/bhp/logitech-driving-force-gt
Of course this is just my opinion, because I've used one. I sure others will recommend other wheels.
Good luck
P.S For instance, I bought my current G27 brand new from ebay, and it was delivered direct from Logitech in the Netherlands. It cost me £150.00, a lot cheaper than list price.
I guess the guy had some sort of deal going on with Logitech.