Many moons ago I found Futureme.org, and it's become one of my favorite things on the web. It still exists, it still works.
The premise is simple: write yourself (or anyone really) an email, set a date in the future for it to be delivered, and then... wait. It's like making yourself a tiny time capsule. I initially found it useful for little bets and predictions, but once my son came into my life I began to write lengthier emails about the way I was feeling at the time. So, it has become a nice alternative and supplement to my regular journaling.
The best part of the experience for me is that I've mostly forgotten about all of my letters, so when they arrive, it's unexpected. The farthest one out for me will arrive in August, 2031.
I just hope I still have my email address then.