I don't know of any documented list of timers (or interrupts for that matter).
Some libraries seem to "take over" all the hardware (SoftwareSerial comes to mind with pin change interrupts) whilst others seem to use a minimal amount (eg. Tone, and Servo) and then "make do" with interrupts. However of course the expense of saving a timer might be that you use an interrupt instead.
I don't know if there is a simple solution, except to check on a case-by-case basis. For example if two libraries only use timer, that could be good, but what if they both use the same one? Or both use the same interrupt to share the timer? Or even if that doesn't happen the interaction between them slows things down too much?
Personally I usually code my own pin-change (or external) interrupts, and go to the hardware for my own timers. I know that might be re-inventing the wheel, but at least I am aware of exactly what resources the sketch uses.