Zonda
Don't dismiss the Sigma 180
http://www.sigma-imaging-uk.com/lenses/macro/180mm.htm
I have had one for about 8 years now, and it it is never off my 30D during the season (I have a 20D for other stuff).
It is a really robust bit of kit, having ben seriously abused by me during it's lifetime, and still giving really crisp images.
The Customer Service from Sigma UK is superb as well - a very important consideration.
I sent it off for a small repair a few years bak, and it get fully serviced and came back "as new" for about £40.00 (IIRC).
It is longer and (marginally) heavier than the 150 Bugma, but gives that little extra working distance.
This is very useful as I almost never hand-hold, and the extra distance when positioning a tripod and head is really useful.