I used one of these
http://www.anandtech.com/show/2585 for a while that was a hangover from before. Eventually I ordered a newer computer
http://www.sonystyle.com/webapp/wcs...0151&langId=-1&categoryId=8198552921644784015
I got it because it was the cheapest out there that would give me a fermi video card and 1920 pixels on a horizontal line. Consequently a few days after I ordered it my previous laptop started to violently crash due to some hardware issue with the video card (nice timing on the order!)
My suggestion is as follows - my laptop is nowhere near "too heavy" to carry. You will be doing a significant amount coding. If you don't have eyesight problems and can deal with high resolutions, get a laptop with a 1920 horizontal resolution (i.e. 1080P resolution, or 1920x1200, although those are almost a dead breed... and hence horribly overpriced). You want all the horizontal space you can get. Vertical space is also nice but not as crucial.
I am quite happy with my current laptop. I dual boot W7 and almost stock Ubuntu 10.10 (needed a few tweaks for vid card and sound card, 11.04 should be fine once I upgrade), and this has been a very good setup, at least for me.
Don't get a mac. They look pretty, and a 17 inch macbook pro is one of the computers that offers 1920x1200 resolution, but you pay a disturbingly horrid premium for the shiny plastic. You actually pay a ton to get outdated hardware components and to be forced to put up with apple's monopolistic inefficiencies (how's the reception on that iPhone 4?). Not to mention that there's no advantage to having one, aside of course from looking damn cool.