Your tank is pretty much reached it's limit as far as large growing fish if the angels are the large variety, I'd urge caution on adding more. Smaller fish might be a better idea.
To directly answer your question though, crosshatch, bluethroat, pinktail and niger triggers would be considered "reef friendly" and not as aggressive as most of their counterparts. That said though, any fish has the potential for trouble reef safe or otherwise.
Here is a good article that should help you out.... Triggerfishes
by David A. Crandall, M.D.