I'll vouch for Airbrake. It does an excellent job of identifying patterns and grouping similar errors, tracking resolution across deploys, recording request context to help you figure out exactly what was going on while avoiding spamming you with error messages.

I haven't had much of a need to look at logs since I started using Airbrake three years ago. For the price, it's really hard to beat the value when you compare the price to various log aggregation systems.