Lightweight xlock alternatives?

[Remo Inverardi <invi@your.toilet.ch>]

Is there a lightweight xlock alternative? Actually, I just want to lock 
my X session, so I don't have to logoff when I leave my office to get 
coffee. Xlock with the "-lock blank" parameter is about what I'm looking 
for, but it's *way* to big.

Thanks, Remo