I ended up going for the Nikon based pretty much on "feel" in my hand. I've got little girly hands (said in a deep voice) so the smaller nikon just felt better when I picked it up. I figured I'm going to get more value out of a comfortable camera than a "better" one that I never use.
My dad has the Sony a200 and on paper its pretty much the same as the Nikon but £100 less. For me it just doesn't feel as comfortable or easy to use. The Nikon also does give some pretty good guidelines as to what you're doing wrong when you're about to take a photo and it has a cool graphical display showing you what the shutter and aperture are doing so that you don't get confused by f numbers and shutter speeds which don't really mean much to the untrained eye. Great for the beginner
Basically, set a price limit, look at everything in the range and weigh up the goods and the bads and then work out if you're willing to spend a bit more for a few extra features...... there is always a camera that is just £50 more so set your limit but be sensible on considering extras and keep an eye out for deals. Don't right off the high street - I got mine from jessops and it was as cheap as the internet and there is a branch in every town for backup.
Finally - and I can't stress this enough - don't listen to a thing the salesman has to say in jessops, currys or pc world..... more mega pixals isn't that important, Sony aren't just good at making TVs and my computer SD slot wont read SDhc cards!!!! Do your research online, check out the reviews (often side by side) and go into the shops and physically hold the cameras and take pictures.
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Eco-warrior