2 weeks is standard. As Phoenix86 said - if you live in an at-will state you may screw your sell over.
True story: My previous employer - writing was on the wall, I could either be the glue that held the place together while getting reamed sans lube for shit pay, or I could walk. I chose the latter, got an offer for 50% more money, better benefits and paid relo. I wrote my resignation pending 2 week notice, gave a copy to "HR" (lol) and my manager. My manager knew it was coming. I told my manager I would be more than happy to help train whoever they bring in to get them up to speed and finish up what I was working on. I also offered to work as a consultant after the fact to keep projects going if need be. He was grateful for the offer, but obviously saddened because he knew the owner would fly off the deep end.
So he called the owner of the company to break the news - their last developer was putting in notice. Half an hour later I was told verbatim what the owner said over the phone: "You have one hour to pack your shit and leave." My manager at that time said in retrospect that he should have just "filed" my notice somewhere on his desk and forgotten about it for the next two weeks.