In Israel (at least in Jerusalem) they used to have a really neat system (I haven't been there for a while now). You had two ways to pay:
1. Previously buy parking tickets with scratch-able time and date fields. Scratch off the date and time from a previously bought ticket. Put ticket in window. Each ticket is good for 1/2 an hour, so if you need more time, simply use more tickets.
2. Previously acquire and "charge" an electronic card/display gizmo. After parking press a button on it, this starts "eating up" time and showing that it is doing this on a the display. Place device in window.
When you get back to the car, stop timer.
I guess the device could be hacked, but it's just like any subway card with a big fat display and it knows how to eat up credit at a particular rate.
The main down-side is that there has to be a single price of parking in the municipal area. The other downside is that you have to buy these things in advance. But the ease of use are quite amazing, and with the electronic device, you do not have to guess the amount of time you need, you pay what you use.