I just noticed that this suggestion is mentioned several times on the wiki:
http://macromates.com/wiki/Suggestions/GUI
(see the contributions of John Lianoglou and Sascha Brossmann)

2006/2/8, Charilaos Skiadas <cskiadas@uchicago.edu>:
On Feb 8, 2006, at 3:44 PM, Ned Baldessin wrote:

> Suggestion:
> You could tear off a submenu of the gear popup, and make it a
> floating palette, so you can keep an eye on the list of snippets,
> commands and macros of the language (bundle) you're currently
> working in. Seeing them on the side of the screen for some time
> would help to memorize them.

Ah, that is indeed a nice idea. I usually keep the Bundle editor open
for those purposes, but having an optional floating window with the
commands from a bundle, together with short descriptions of what each
command does, would be ideal.
I am guessing that could possibly be a plugin? I don't know.