My 3 favorites are:
1. Afallen tree with lots of branches to sit in. I try to find one with a branch to sit on where I can lean back on another one to pass the time, and one I can use as a shooting rail.
2. The other afternoon I pushed my way back into a cedar tree and just snapped off a couple branches to provide a better place to sit and lean up against the trunk and give me some shooting room. I snuggled up in there, took a nap for about a half hour, then shot a nice buck about an hour after that.
3. Sit up against a large tree on top of a tall creek bank.

I use all 3 of these with no problem, I have a doghouse blind but I just don't like being confined like that I want to be able to just crawl 5-10 feet this way or that to get "the right shot" if need be.