I can be quite funny, but I need a prompt, so no stand-up, too much of a blank slate. I can't resist being funny when doing things like live blogging, responding to a thing that's happening with quips. Is there any established comedy form that incorporates that sort of quick-fire spoof commentary? The only thing I can think of is those video voice-overs Hugh Dennis used to do on Mock the Week.
Depends what your interests are really I guess. You could do short videos about news items in a Charlie Brooker style for instance. Or even do the Hugh Dennis voiceovers in your own style, but the amount of clips you'd need and the editing etc may take too much effort. Also things like co-hosting a radio show or a film review show etc.
You could look into doing short sketches about things. If you're interested in music you could do a blog talking about new releases, or if you like sport you could do something similar to The Fiver section in the The Guardian. You'd still be making quips they would just be written.
Things like stand-up, TV etc is more difficult to do if you're just starting out on your own but there's no reason you couldn't transition into to it after a while if you wanted to (after enough practice you may start to become your own prompt and arguably stand-up along with Brooker's Screenwipe/ The Daily Show style news reviewing would be two most suitable comedy forms I think).
Take a look at Mystery Science Theater 3000. It was a cult TV show that basically consists of three characters watching old B-movies and keeping a running commentary, one of the funniest things I've ever seen.
The main guys behind it now do Rifftrax, downloadable commentaries for modern and classic movies, might be something you could try, just watch stuff like awful films and trash TV and record whatever comic musings come into your head.