Originally Posted by 3alarmer

...130mm rings show up all the time at the local co-op here. I have a collection in various tooth counts, but the ones that are not either 52, 53 or 42, 39 don't show up as often.
If you want to try different gearing combinations (or different setups, like half step with something like 52/49 or 51/48. you're probably better off buying the less commonly encountered ones online in the Vuelta line mentioned above.

What rings you might want depend entirely on what you are trying to accomplish in terms of gearing, and the sorts of riding you plan on doing. Do some rough gearing calculations on one of the online gear calculators.

But you see 52/42 a lot because it is a good general purpose combination for a 12 speed.