'Better than the kit lens'
You could invest for the very long term in one lens - 17-40 f/4 L for £630. It's not the biggest range, but 17 is very wide for most people and 40mm will get you nice head'n'shoulders portraits. It's a lens that you can easily find a buyer for if you don't keep shooting and you could still get the 50mm 1.8 for something light and fast.
More versatile, more complete:
The 18-55 IS is a fine choice. Jessops list it for ~£90 but you'll find it cheaper elsewhere.
Everybody will recommend the 50 1.8, because it's so fast and so cheap - £90. And for just a few pounds you should definitely get an off-camera flash cable and play with light.
I really like urban and landscape too. So something 'fast' (lets lots of light in) for night shooting, and something wiiiiide is fun too. I own the 28/1.8 (£389) but the 2.8 is £170. Maybe a 10-22, or similar later on.
I'd also recommend a tripod at some point if you're going to seriously shoot landscapes or at night. You can, and should, spend a lot on one. Say £100? plus head. But it's better than spending £40 three times.
I like lowepro bags, but don't get something too big. I've made that mistake and never carry it, or when I do, it's too heavy and I don't use much of what I take along. Now I pack 2 lenses and can easily shoot from 8pm till about 3am when I get caught up in the city and surrounding areas.
So you could kit yourself out for well under £650. But don't spend too much on CF cards unless you intend to move up to the 7D or 5Dmkii as the x00D's and x0D's all use SD cards now. I found a spare battery was essential for my 400D but maybe a bad investment if you're sure you're upgrading.
I like making photos and sometimes I think I'm getting better... then I realise it doesn't matter. I like making photos!