Trivia can be fun:

Total mileage (can also be used for maintenance intervals)
Travel time (timing yourself is a good way to develop conditioning)
temperature - not that you can do anything about it, but it's nice to know sometimes
cadence - again, it's about conditioning and training for some of us
clock - goes without saying

I have a small, unassuming computer on my stem that provides these and other data about my bike, my ride, and my environment - it all enhances my experience - for $25, it's worth it to me