(i really wanted to stay under $500 but i was having trouble finding something)
You can even get $400 notebooks.
They just don't do very good running modern games.
I think that Lenovo IdeaPad Z570 with it's Core i5 2450M 2.50GHz CPU & Geforce GT 630M graphics card should run Diablo 3 on medium graphics.
NVIDIA GeForce GT 630Mhttp://www.notebookcheck.net/NVIDIA-GeForce-GT-630M.63761.0.html
I'm not seeing any deals that are better ATM.
How soon do you need to buy the new notebook?