URL Shortner Plugin?

I would like to know if anyone knows of a plugin that will accomplish what tinyURL and others do. Basically, I want the permalinks of my posts to look like this:

/w8mi

instead of

?p=232

The reason for this is that I am building a site which will have many thousands of entries and I need the URL’s to be as short as possible. Random combinations of letters/numbers gives me more permutations than just numbers.