Solve Issue of Camera looking through walls when in them

Hey guys! I know this is a question which is mostly game-specific, but I thought it's still worth a shot.

Probably everybody here knows the problem that when one is close to a wall, the camera "enters" the wall.
Now either one is in the wall and sees through the wall, resulting in a wierd view. (Bad, but not worst-case) The other (worst-case) possibility is that the camera goes to the other so that the player (as a person) can't see his avatar anymore.

My question is, how did you guys solve this problem? (Answers which only work in your game are very much appreciated and will be voted up)