I've been very interested in the flash form for a long time. I think I really jump started myself into serious writing years ago with a series of very short pieces I called "Guns and Bugs." Now, I'll use short shorts to prime the pump when I'm feeling stuck, or to give myself a sense of closure if I've been working on a long piece. Both my Seven Sentence Story post and the Natural Narrative vs. Literature dealt with creating flash fiction.
Other resources for writing flash fiction include G.W. Thomas's article on "Writing Flash Fiction," Jason Gurley's "Flash What? A Quick Look at Flash Fiction," an interestingly visual approach at "Writing Flash Fiction Using Bubble Diagrams," there's "Ten Reasons to Try Flash Fiction," and a nice interview with Michael A. Arnzen "On Writing Flash Fiction."
Also, there is the vastly underpriced short-short story subscription service Bruce Holland Rogers offers. If for no other reason, you should click on this link to see the Alan M. Clark illustration for it.
On another note, I saw a pleasing reader reaction to Summer of the Apocalypse here.