I'm in the market for a new laptop. My current one (MacBook) is starting to show it's age; I run Ubuntu on it, but there are a number of incompatibilities that are starting to irk me, and the computer itself is starting to have hardware problems.

I don't want to buy a new mac - I'm after something with a bit more performance. I want at least 15" of screen real estate, an Intel i5 or better processor, and at least 4GB of RAM.

My most likely choice is Dell (perhaps a Studio 1555?) but I would like to know what laptops people have had the most success in using with Ubuntu?