I visited Montreal for OOPSLA in 2007. They have a really neat parking meter system. Instead of a traditional mechanical meter at every parking spot, each spot has a label (e.g. "J 103") and there's a computerized kiosk on every block where you can pay for your spot for a certain amount of time.
All the kiosks are networked, too, so you can pay for your spot from any parking kiosk in the city, not just the one on the block where your car is parked. So if you park somewhere and walk across town, you can still easily pay for time on your spot.
There's a small-annoyance hack available with this system.
If you pay for three hours of parking at "J 103" at noon, the meter will expire at 3pm. If you pay for one hour at 1pm, the meter will expire at 2pm. The amount of time you can legally park is not cumulative, but takes effect at the moment you pay, for the exact amount of time you pay for.
So, if you wanted to put someone at risk of getting a parking ticket, wait until they park, then pay for 15 minutes of parking for their spot. After the 15 minutes are up, they are illegally parked, regardless of what they paid before.
(At least that's my understanding of what was explained to me by my host. Corrections welcome from Montrealers who know better than me.)