DeWalt or Makita are always a safe bet, Hitachi can be good too. I you have the money and you want something that'll take a beating and last forever, go with Milwaukee.
A quick google search of cordless drill reviews will yield loads of info.
fmahovalich's advice is good as well, two batteries are better, look for Lithium Ion rather than NiCad batteries, they are lighter and hold more charge.
If you think you night be drilling into concrete, think about a hammer drill. You can turn off the hammering option, making it act like a normal drill, but if you're going into concrete, you'll be glad you have a hammer drill.
And don't call it a portable drill, unless it's a drill press, it's portable, you're looking for a cordless drill
I'm envious BTW, I haven't had a good excuse to buy a new tool in ages.