What is a good opening in Blokus?
Ever since I learned about "the Barasona opening", I've had a hard time not starting all my Blokus games with it.

The basic idea is that your first four pieces leave no possibility for an opponent to move "through" your corner, without the use of his one-piece.

The pieces you use are F, X, W, and then N or Y.  You can see a picture of the Barasona in action here: http://boardgamegeek.com/image/112251/blokus.  

Of course, the problem with the Barasona is that, while it provides a disincentive for other players to move towards your unprofitable corner, the moment the other players realize this they will probably all start using the Barasona themselves, and you're back to square one.  Blokus is an arms race!

Hope this helps!