I would suggest going to a camera store and seeing what you find is suitable. Silly comment you may say but in actual fact every camera make has a different layout and you may prefer one make to another. How they sit in your hand can make all the difference.
When choosing a camera do look beyond just the camera and look at the pice of the lens that can fit it and the range of lenses, also budget for the cost of a memory card as they don't come with the camera. Suggest a Sandisk Extreme 111 or 1V with 4 gig as a starter, any slower memory card and you could come up against camera pause in continuous shooting mode due to transfer rate from camera to card.
I can't say I am in favour of the D90 as it combines movie mode as well as stills and although I have never tried one out, I would prefer a camera to do stills only (at this stage I am desperately trying to fish a fly out of my cup of coffee) against a duel mode camera. Having said that it depends on what your main photographic theme is going to be.
You can find makes cheaper on e-bay from abroad but I would advise against buying due to the warrantee may not be accepted in the UK, presuming that is where you are. Also sending it back if it goes faulty could be costly.
As i said at the beginning trying out in a shop is your best route, you can read writeups till your blue in the face, this camera has better this than that camera etc. Whatever you choose as soon as you have made your purchase you will see something a little bit better at a slightly higher price, thats sods law.
Remember you don't have to buy from that store you may find that particular camera being sold by another UK company at a lower price so don't get carried away with the " must have now " syndrome.
Having owned Nikon D70s then D200 and now D300 (which I absolutely love), one thing I would suggest looking into is the controls. With my previous cameras I had to constantly dive into the menu to alter settings which was a bind to say the least, with the D300 all the major adjustments are situated on the body which is far easier, something to seriously watch out for. I can't speak for other makes and their layouts as I am in the Nikon camp
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