If you're looking for saving a lot of money, and will only be using it for basic usage, I'd recommend the Asus eee PC X101H (which I'm using right now).
Not only is it amongst the cheapest netbooks on the market, it's also the second thinnest (the thinnest being the X101, which uses a small capacity SSD), it's extremely well built for the money, and due to it using the Pineview platform for it's CPU and also using DDR3 ram, it definatly runs better than the average netbook.
If you want more ram memory in it, it's extremely easy and cheap to upgrade it to a 2GB ram stick. (just a case of removing a panel from the back, popping out the old stick and in with the new)
Edit: It's currently available from Argo's at around 199 pounds, although I would've thought you'd be able to get it cheaper if you search around (I got mine for about 185€, or 154 quid)