Do you need a bit more "oomph" in the processor or is an Atom going to be fine? Personally, I needed a bit more power from the machine as I wanted to be able to do more than just open a couple of browser windows at a time so I went for the ultraportable range with the SU range of low power pentiums. I tried the HP DM1 which looks nice but is NOISY and constantly speeds the fan up for no reason. I moved across to the Acer 1810tz as much as it pained me to buy an Acer and to be honest it has proved much better than the HP and Sony I have used! Runs quiet, has about an 8 hour battery life and I've kept it.
The HP ultraportable has a netbook cousin called the 311c. Exactly the same outside, but an atom on the inside. It looks like there is a software hack for the 311c to stop the fan from speeding up all the time, but check the 311c thread here. I personally didn't like the clicky buttons or shiny hard to use touchpad on the HP range, but maybe you will like it. It looks nice though!
Didn't go down the atom route so can't help further than that really. You need to say what you will be using the machine for and what you expect of it and what your max budget is.
