Topic: log file monitoring

What does everyone use to monitor their rails log files for erros? I would like a system where I can whitelist log entries, and get emails about the rest and periodic intervals. The fact that the entries can be multiline makes things a little more difficult. I'm of half a mind to write my own parser in perl (or wait, I guess ruby would do), but wanted to see if anybody had any tool they currently use?

Thanks for any suggestions.