I currently use a combination of Car Minder for the iPhone - it's only $2.99 but limited functionality - and Excel spreadsheets. Ideally I'm looking for something that will track all service for up to 5 vehicles. MPG tracking and ability to export data into a common format (Excel, comma delimited, etc.) would be nice. I would also like to be able to generate a variety of reports to see how much I am spending per vehicle, perhaps showing "regular maintenance" different from "add ons" - i.e. an ARB bumper is a large cost for my truck and I want to record the expense, but it's certainly not a maintenance item.
Here are a few I found from a quick google search - just curious if anyone has used these or others.
EZ Maintenance - $40/month
CarCare Automotive - $40
Innovative Management Systems Auto Maintenance Pro - $35
KZ Software Vehicle Manager - $35
Automotive Wolf - $20-30