Well with that budget you can either afford a 23in 1080p IPS type panel monitor or a 24in 1080p TN type panel monitor.
The IPS (like
this one) offers better overall image quality (specifically more accurate colours and wider viewing angles) - though it isn't as responsive as a TN panel in games - so you may notice ghosting when playing fast-paced games (it really depends on how sensetive to ghosting you are whether this is an issue).
On the other hand, a TN panel 24in (like
this one) is a bit bigger than the IPS (though has the same number of pixels) and is more responsive than an IPS - so generally better for fast paced gaming as you are less likely to notice the ghosting. However, the colour accuracy isn't as good and the viewing angles are much worse than an IPS (so that when you look dead-on a TN panel and move your head a bit you will see the colours shift a bit, also you are likely to see some colour banding at the extremes of the screen).
If you would like an IPS that is also pretty decent at playing games then I would have a look at this
Dell U2312HM for £190. It has the benefits of a nice quality E-IPS panel, but also uses a well-controlled overdrive impulse so the response times are pretty good and should be fine for most gaming. Quite a few users on these forums have the U2312HM (and the earlier version - the U2311H) for gaming and find it great - it's worth having a search for these model numbers in the monitors section and see what people say.