Of the things that are sometimes using a FP for, I'd say at MK meet & greets with anyone but Mickey, Winnie the Pooh, Buzz, Small World, and Jungle Cruise all have a pretty good shot of turning up easily. HM and Pirates are probably next most likely, as well as Splash on a rainy day. Any ride at MK except 7DMT is pretty darn turn up eventually if you are crazy enough on the refresh.
At Epcot, SSE, M:S and Living with the Land sometimes are worth using a FP on, even the Seas can be too, and those come up regularly. Everything but FEA should pop up eventually if you refresh for a bit. Frozen can be hard to get day of.
At DHS, everything but Slinky Dog will be available for some point that day when you get to the park.
At AK, Dinosaur and the raft ride are the easiest of things that are worth using a FP on.