As for short videos - I'd suggest parts of MEPs, trailers, and comedy videos, many of which are short, and search by min/max filesize (shiny!). Also, many WMVs are encoded horribly small; I did one once and it crushed a 30MB regular encode into like 12MB.
![Confused :?](./images/smilies/icon_confused.gif)
Quality is hit or miss, but the filesize
does tend to be smaller.