I'm with 5. Older refurb IBM are great. Don't bother buying new ones (Sept of this year of later) as they are from new PC maker Lenovo out of China and not yet proven. I have worked in IBM and Dell environments (both between 500 to 1000 pc units) and I would rather work on an IBM then a Dell any day. IBM is easier to upgrade and repair. Dell might as well buy a new one if something breaks.
That being said my newest environment is running nothing but Fujitsu laptops (120 units) can't say enough good about them. All P4's with nvidia video, they run cool and run the graphics we use daily quite well. Not fitting into your budget new but here are some links to used on the bay
http://computers.listings.ebay.com/Laptops-Notebooks_Fujitsu_W0QQfromZR4QQsacatZ18792QQsocmdZListingItemList