Whatever distance/interval, I would tend these days to do progressions meaning, starting out a little slow and building up speed over the interval, finishing each interval faster than I started it. I don't know if this is better in the physiological sense, but it's a good habit to get into mentally. I mean, if you're interested in strong finishes in races.
I've used and enjoyed a "gear shift" method: start in first gear (not much more than a slow trot), then second, third and fourth or up to fifth gear, which should be close to full-on sprint. 10 or 20 and up to 50 strides per gear. I would actually count outloud while running.
For more basic intervals, my favorite distance was always 6x600m with a good but not complete cooldown between intervals. 800 is just a tick too far and 400 too short (for me).
Hill repeats are of course awesome. Run up, trot down, turn around and do it again ... rinse, repeat. (And do a couple of them backwards! Double the awesomeness, really!)