Finding a good gaming laptop under the $700 can be pretty hard as good gaming laptops are way above that range. But anyways there are some decent options always. Here is an excellent page listing many laptops for gaming under $500 :
http://markmorgangenius.hubpages.com/hub/Cheap-And-Best-Gaming-Laptop-Under-500
I would recommend you see this page and also the embedded videos in it.
If you are looking a laptop solely for gaming purpose for playing any modern heavy games and you are tight on budget then I would recommend
1) Asus G50Vt-X5-RF Notebook PC : This is one gaming beast. I had this laptop and it works excellent. It can handle any sort of hard core gaming very well. See the above page it has a short review about it plus a video review for it. This laptop has a 15.5" display with resolution of 1680 x 1050, Intel Core 2 Duo 2.53 GHz processor, GeForce 9800M graphics and a 4 GB DDR3 RAM.
Some other options would be XPS series from Dell. My friend has a XPS 15 L502X. It is an excellent laptop which I would call a full multimedia package. Get a i5 quad core processor, NVIDIA GT 540 M graphics. This laptop has JBL speakers with a subwoofer. It can handle games very well, excellent for watching movies, listening music. It would be best for anyone looking for a laptop for regular use along with occassional gaming.
Visit the above mentioned page to get some more options.
I hope that helps
Visit Here:
http://markmorgangenius.hubpages.com/hub/Cheap-And-Best-Gaming-Laptop-Under-500