I'd go for a dell studio series, you can get them with a nice core i7 for a nice price. You can choose to have Ubuntu pre-installed. So the operating system costs are a lot lower. You can customize all the hardware, i'd say these are perfect. Dell offers a lot of great benefits and their prices are great, even better with discounts which they offer a lot. My friend got one with an i7 which he uses in university all the time. He's running Ubuntu 9.10 without problems.
If these don't suite you, don't forget to check out the dell inspiron series, I find these superb as well, a great price performance-balance.
Not to be a hater, but don't buy an acer laptop. I love acer desktops and lcd screens, but I had real bad experiences with their laptops.
Good luck, and by the way, try to buy one with an nvidia graphics card. (Personal driver experiences -> they're great, superb over ati)
EDIT: About dell offering Ubuntu pre-installed, I read this in a new article, but browsing the site I haven't yet find a way to choose this.