I know of the standard western technique where the beats (quarter notes) are numbered and eighths are vocalized as 'and' and sixteenths are vocalized as 'ee' and 'uh' (One-ee-and-uh Two-ee-and-uh).
I've also come across "Ta titi Ta Ta", but don't know how to subdivide it further.
And in the liner notes to some Sheila Chandra recordings entitled Vocal Percussion, there's reference to a traditional Indian system (or several) of associating syllables with rhythms?
What other systems exist? Note: the more complete, the better; does it have provisions for triplets or higher compressed-time figures?