I have a single sheet of paper with notes on the most recent maintenance for all my vehicles, that is how I keep on top of service intervals. I check the odometer periodically and compare it with the notes which indicate the mileage of the last service. Also I use trip meter #2 for tracking oil & filter service intervals, kind of redundant but the Tacoma has 2 trip meters, so why not.
For long-term maintenance history, I have Word documents with everything I've ever done to all my vehicles, and I make regular entries in the owner's websites (Chevy owners/Toyota owners).