Which B&W line are you looking at? They offer lines in a wide variety of price points. Their 600 series is their meat & potatoes line but unless you're looking at the 600s or 601s (the two smallest ones in the range) I don't think you'll be able to put together a whole set within your budget. The DM602 S3s (a big bookshelf) are close to $600/pair.
I'll second the comment that B&W is QUALITY. They put together really solid, beautiful speakers that sound fantastic. They're not everyone's cuppa Earl Grey, but I personally like them a lot. I haven't auditioned the 300 series, though they're probably fine and they're definitely closer to your budget. Better check them out yourself.
Does your budget cover a 5.0 set alone or does it need to cover a sub too? (I'm assuming you're doing home theater and not just 2 channel stereo.) If it needs to cover the full 5.1 set with sub, you might have trouble finding something within your budget that looks as good as B&W but still sounds good. If you're willing to go with plain black boxes that sound amazing, DEFINITELY check out SVS's new SBS-01 5.1 system. About $900 for 5 speakers and a sub, and believe me that PB10-ISD sub is AMAZING. For a bit more Ascend's stuff is highly recommended though I haven't yet heard them myself (will soon though). Axiom might be a good choice. Not sure what you can get within your budget but they do look good and lots of folks seem to like them.
Good luck.
