The International Lyrics Server is a great place to search for pop lyrics. if all you know is a few words from a song, use their fulltext feature. For country, try Cowpie.
For folk songs, search the world-famous Digital Tradition Folk Song Database right here at the Mudcat Cafe. Just enter a few words in the search box at the upper right corner of this page.
After you've tried all that, then try posting your requests for folk songs here in the forum. Make sure you give a title to your request thread that identifies your song somehow. Threads titled "trying to find this song" just tend to irritate people. For other songs, you'll get best results if you post a request in the alt.music.lyrics newsgroup.
Grump, grump.
-Joe Offer-