I've been looking for Eyefinity compatible monitors for the last few weeks and with Dell's 20% SMB monitors voucher available at the moment, the P2310H seems to give the best bang per buck at £174.
It may not seem as cheap at the ST series monitors posted recently, but the P series monitors offer features that aren't found on the cheaper ST series:
* DisplayPort connection (req'd for Eyefinity)
* USB hub
* Ability to attach to a VESA mount
* 3 year next day panel warranty
It's ideal if you're looking for an Eyefinity setup, and you can pick up 3 matching 23" screens for £522 (around £505 after Quidco).
You can always mix and match a P series monitor (using DisplayPort) with 2 cheaper ST/E series monitors for a cheaper Eyefiniyt setup. If the P2310H is a little too big, Dell offer a 21.5" P2210H for £155.34.
AMD have used the panels at their Eyefinity events so they should be pretty good.