Graphics card help

Okay, so I've had this computer for about a year now:

http://www.pcworld.com/product/552981/dell_inspiron_14r_model_n4010.html?p=specs

It's not a bad little PC, but when I got it I had no idea I'd really want a PC that I could game on. It runs older games no problem (i.e. Diablo II, L4D2, Killing Floor) but I now realize that the graphics card it came with (Intel(R) HD Graphics) isn't up to snuff with the games I'd like to get (Skyrim, Diablo III, Just Cause 2). So what kind of graphics card should I get for it, and where can I get it installed? I don't want to break the bank, so what is something I can get a good deal on?