The tokens I have chosen are 0.984 inches in diameter. These are called 'quarter sized' tokens, but they're actually just a bit larger than a quarter. I picked up a batch of old Chuck E Cheese tokens on Ebay. One nice advantage about 0.984 tokens is that you can usually convert a quarter mech to run with the slightly larger size. It requires a bit of filing and adjusting, but it is manageable. Plus, I already have a bunch of quarter mechs in the machines. It is possible to buy token mechs, but they can get pretty pricey in a hurry ($10 to $15 or so each on ebay). If you have the patience, converting your quarter mechs is the way to go.
In my case, this has been an interesting task, since many of my machines have different coin mechs, and many require different adjustments. It's a lot like solving a puzzle at times. Here is a basic rundown on a run of the mill metal mech:

Then comes adjusting the cradle. On this mech, I actually ended up removing one of the cradle pieces in order to get the tokens to pass the cradle area:

