Depending on what you want, regarding voltage regulation and current compliance, these can be quite common and easy to build. The usual form is found in cameras (with a flash) or in emergency strobe lights. They typically use one BJT, one custom transformer with a center-tap on the side that the BJT is on (primary), a diode on the secondary side, and a capacitor. This produces in the neighborhood of 300V for the flash lamp, but since 4kV is needed to trigger it, they follow it up with a trigger transformer (available even at radio shack) that accepts 300V and produces 4kV, which fires via an SCR or similar mechanism. Although your source voltage is different and probably at least three times higher than a camera or emergency flasher uses, you could probably avoid the extra step by using a properly wound transformer in the first place, and get your 1000V directly without the trigger transformer. It won't be all that well-regulated, though you could add a chain of NE-2's to get something "not too bad." (I did this for a Geiger counter, for which purpose that kind of regulation was just fine.)
What shocks me most about your question, though, is that you start out saying "DC-DC converter" and then ask for the "greatest AC power output." These are not generally congruent requests and you say them in successive sentences. I'm guessing you know very little about the terminology and aren't saying what you intend as the application. Expose _why_ you want this.
Edit: I see you are looking to make a Marx generator, from another of your questions. So that explains things a little better. See link below, bottom of its page: The 555 function can be replaced by a few transistors. You could also use a motor that rotates fast and chops up the DC, too, using simple metal contacts that make brief connections -- that would be the "old" way to do it. Old radios used to use something called a "vibrator" and these worked on 12V. So that might be another option to consider. (I've included some links on that, including a schematic for making a transistor version.)