I'm looking into getting a 100 f/2.8L or 135mm f/2L, to do some portrait/ macro work. I won't be using the Macro a ton, but would like the feature. As of today, my budget only allows for one or the other, so I could use your help in deciding between the two.
Right now, I'm using a 24-70 f/2.8L Mark I, and a 50mm 1.4 on a 50D Body.
The 135L is the best portrait lens for the money. You can get pretty close for light macro work with extension tubes if you really want.
If you do more macro than portraits, The 100L is for you.