Download Google's toolbar and allow the PageRank option. Then look at the site's PR value. It will be a value between 1 - 10. 10 being the best. Anything with a little green in it will be helpful, but more green in the toolbar meter is better.
While page rank can be a great indicator, of a site that would be a good link, I wouldn’t recommend on relying on that alone. Try to pick sites that our really related to your site, sites where you might actually get traffic. Those are quality links.
Think of it kind of like if you woke up tomorrow morning and there were no search engines where would your traffic come from? If you choose quality over quantity with links I can assure you in the long run you will come out ahead.