I love my Casio watches. I have an F-91W and a B640W.
The F91-W is super light and you basically can't even feel it on your wrist. Sadly after three years the pin holding the lock in place broke, and I still have to change it (I am using the other one).
I'll probably join the G-Shock bandwagon soon, I'm intrigued by the bluetooth-enabled G-Shock watch.