Since these depend on location, operating systems, who knows what, the user will have to run a function from their current terminal to discover the timezones available to them. See ?Sys.time for details.
Two locations for time zone info mentioned by stackoverflow are
"R_HOME/share/zoneinfo/zone.tab" (R_HOME is the directory R is installed in)
This information may be stored in different places on different operating systems
R's ?Sys.timezone describes why this is pretty much impossible
Hmm, I don't think that's completely true, since everything basically uses the standard Olsen TZ database. At least a pointer to that would be useful
I'll place some useful examples of common timezone classes in the tz help page
Added timezone examples for common Olson timezones. Fixes #79.