I've seen a few reviews of these cards, which seem to be aimed to fit into the £150-300 bracket, although no actual internet dealers seem to be selling them yet. Might be worth keeping an eye on for prices as they are put up shouldn't be long now.

http://www.engadget.com/2012/03/05/amd-radeon-hd-7870-and-7850-review-roundup/

 Unless you're despite for a new graphics card I would wait to see what Kepler does to prices. The current top end cards from AMD are fast but are overpriced IMO

Release dates should be soon , HD7870 does look like a very good card but as Shaun said it is worth waiting for
Kepler to see if prices do drop.Prices are set to compare with present Nividia cards(HD5870 is comparable in performance
to 580/570 especially when overclocked) so if Nvidia decides to release Kepler with competitive prices it should drop the prices.
Prices for HD 6970/6950 have dropped a little & may drop significantly when Kepler is released & could be a really good buy.

Some have stock in or pre-order options.

TBH these are more than likely going to be wasted on a single standard 1080p monitor, it should be able to power 3 or more adequately, or at least one    2560x1600 monitor.