I found a cool tool that helps you decide how much your site is worth for someone who wants to buy text links on it.

It calculates the value based on how much traffic you get, link popularity, where the link will be on the page, and other factors. It's in $USD, and isn't definitive, but at least it will give you an idea.

www.text-link-ads.com/link_calculator.php

There's also a tool for bloggers to calculate some mysterous thing called "blog juice".