Now I'm no expert by any means and usually a great deal of my advice is go and talk to people more experienced / knowledgeable than me however, failing this advice there are a good few basics to consider and places to look online.
So first off consider what kind of a player you are, not just in terms of style but equally body size, weight, position you play, how much pain your joints give you etc. This is important as people who are heavier or have poorer joint health usually prefer more cushioning to reduce the impact of jumping on their body. Whilst individuals who play a forward or post role should likely look for more heel stability and ankle support due to the increased physicality of the position.
Conversely if your a small guard who slashes a lot then you would likely prefer a lighter shoe, potentially a low top, with better court feel.
Now of course there's also personal taste and preference to take into account, not to mention how they look. This of course doesn't play any scientific part in your performance but often psychologically feeling like you look like the dogs bollocks helps you play just that little better!
Now personally the following sites are the ones I tend to check more regularly for reviews but it's always worth having a good google (other search providers are available) around before purchasing anything.
- http://blog.blacklotus9.com/
- http://blog.eastbay.com/reviews/
- http://counterkicks.com/
- http://kicksnet.com/
- I know I'm missing an obvious one but can't think of it right now...will come back and edit!
Lastly, go and try them on, even if it's not where you end up buying them from there really is no substitute for doing this as there's no telling how a shoe will fit to your foot. I personally know I went to try on the Nike Hyperfuse after they reviewed fantastically and found where the toe box bent was painful on my foot, tried the Kobe VI and whilst incredibly comfortable I just couldn't trust the lack of ankle support, finally I ended up with the Nike Hyperdunk 2011 which have served me well (pic below).
Nike is far an above one of the easier brands to get in the UK (personally I recommend either Hoopz underneath Footlocker in Oxford Street, London or Nike in Westfield in Stratford City), Adidas can be bought from there website but is difficult to find anywhere else, finally Underarmour is a great up and coming brand but again difficult to get in the UK. Other brands such as And1, Reebok etc are available but tend not to be as strong contenders from what I've seen.
Good luck and happy shopping!