Is there some kind of pwd generator for Linux that has a nice GUI and options like this one for Windows? I know that there is
pwgen, but as far as I know it does not support mouse/keyboard entropy and it does not have any kind of front end GUI's... or does it?
pwgen for Linux uses
/dev/urandom (which is a fine cryptographic-quality random source). The Linux kernel accumulates entropy internally (it used to use mouse and keyboard movements, though recent versions have discarded this in favor of better entropy sources); it does a better job of it than a program that merely asks the user to wriggle the mouse.
An better one is APG that optionally uses
/dev/random and asks for keyboard input (in principle, to randomize even more, though isn't actually useful on modern operating systems that collect entropy internally).
If you want a GUI, there's jpasswordgen in Java, so it works everywhere.
IMHO, I don't see the usefulness of using a GUI for this. The goal is to get passwords, and pwgen/apg can even generate nicely formatted lists of passwords.
KeePass (and KeePassX) are password safes but also allow you to generate passwords using keyboard and mouse entropy.