if you're unsure about which shoes to buy, i would suggest going to a 'proper' running shop and getting their advice as to what works for you. Once you've used their advice, you should buy at least the first pair from them. There is nothing worse than people who use their time and facilities then breezily walk out, to try and find a bargain online. Most local running shops aren't big corporations and need the business.
Once you come to replace them and just want another pair of the same shoe, then it's OK to buy them from wherever. I've used Wiggle a lot and I'd recommend them - they even send you sweets ! There are lots of others that are good too - prodirect running, start fitness etc.
I think it's pretty simple. Go to a reputable running shop, take their advice, try a variety of suitable shoes from a range of brands and go for the ones that work and fit best for you.
Running is a simple and very cheap sport. The only equipment you need is a pair of shoes and a road. One costs you money, the other is free. Within reason I wouldn't bother trying to save money on shoes, it's a false economy.