The 135L is one of those primes that really is just a magic black tube with AF. If this lens doesn't satisfy your needs, consider the 70-200LII. Once I got the 135L, I just can't justify the 70-200 unless your doing action all the time.
The 135L is in a league of its own.
I owned the 70-200 2.8 IS II for a year and it never left my 5D2. I took it out on walks, I took it to the park, I took it to weddings. I never thought that it was so heavy that I wanted to trade it for the F4. Never.
The 70-200 2.8 IS II performs almost as well as the 135L and includes 70-134 and 136-200 as well.
This is not exactly accurate... in fact, the comment the zoom on top of 135mm "includes 70-134 and 136-200 as well" got me laughing. It is like those awful TV commercials "Wait, wait, that is not all!!!...if you call now... you will get on top of the toilet scrubber, this great self cleaning pink toilet brush !!!"
The 70-200 II zoom may cover the 135mm range, but the 135L prime is compact, faster than the zoom at f/2, and above all, incomprable in IQ even wide open.
The 70-200 II may well complement the prime nicely, but by no means is it a substitute for the 135L.