No doc loans are loans where you don't need to state income or assets. You could go with a state asset, no income loan as well.
These loans might be hard to go by as the alternative lending structures are changing as companies are doing away with these alternative loans as the credit of americans is changing. Right now the mortgage industry is plagued witih foreclosures for many reasons.
The limited document or no-document loans are pretty much credit based so you need to have at least a 700 credit score (most likely - some companies you can get away with a 680 but i'm sure that is going to change soon.). Also, getting 100% with these loans might be a little tricky as well. If I remember correctly, my company would only do up to 95% LTV. Our company was extremely lenient in underwriting as well so I imaging that the competition had more stringent underwriting guidelines.
If you want an 80/20 and won't be moving very far (you could "claim" that you are going to commute to work) I would go conventional if you have good credit. Make sure you will have your job so you can submit your necessary paystubs. If you are moving to another state, then you would have to pull the "2nd home" deal most likely which would be a higher interest rate.
If you are looking 80/20 and do not own a home, I might suggest going goverment. There is no PMI and minimal fees (they can be rolled into your loan) and you can get up to 100% financing. Its a great thing for first time homebuyers.