Bazza, here's where I always start thanks to the folks at Tom's Hardware: http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-8.html
The information is updated frequently enough to guide you toward your starting point. If I were purchasing right now I would look seriously at the Radeon R9 290. If paired with another, you'll have no horse power than the top card, the Radeon R9 295X, which costs upwards of $1,500.00 U.S. I just checked the price on the Radeon R9 290, MSI has one at Newegg for $434.99 U.S. This is a 4 gig card.
Check it out!