As I have said before - Mac Book Pro 15" - 

I'm pretty impressed at the specs on the Y400 line from lenovo.  i7, 8gb ram, with a 2gb gpu jammed into a 14" laptop at a $750 starting price.  potential for a dual graphics ugrade too.  Haven't tried it, but it sounds promising and reviews are positive.

There are a lot of decent light weight options, so some more info might be useful:
- software use
- budget
- can you farm out rendering to a school computer?
- windows or mac preference?

Dell XPS 15 best spec:

http://www.dell.com/us/p/xps-15-l521x/pd?ref=2132title

vs.

Macbook Pro 15" retina display $2799

http://www.apple.com/macbook-pro/specs-retina/

Which one would you buy for architecture and gaming?

I would buy an asus

gaming on a macbook?  they allow that now?  i thought that was sort of like autocad with an apple os.  they just don't get along.

There's a similar thread started few months ago with very good advices....

I'm also looking for a laptop for my M.Arch studies.  Budget around $1000 and I really want to use dual monitors (concerned about gpu size being an issue here). Any suggestions? The Lenovo Y400 does sound pretty legit...I'll definitely check it out.

my vote goes to lenovo y500, or y580 (if you can still find it), make sure you buy one with full hd resolution and the extra sli card. there are some good tablet as well, pretty useful if you want to quickly sketch some conceptual drawings and plans.