135mm lenses are typically not overly endowed in the image circle arena.
Originally Posted by Alan Gales
I'd go for a 120mm over a 150mm. You can always crop a 120mm, but it's often difficult to move further back with a 150mm. Specifically, a Schneider 120mm Super Angulon would be my recommendation. Rodenstock's 115mm is also a cracker lens, as is the Nikkor 120mm W; however, these are typically more expensive than the (somewhat of a bargain) Schneider. You will, however, lose a stop with these (I was shooting at night last week with my 120mm f8 and had no issues with focus. Of course, others might not be so lucky).
As for tripod head, if you can afford one, a 3 way geared head is perfect for architecture. I'd avoid a ball head; they can be difficult to use when small movements are needed.
Two other things I'd recommend: a Fresnel screen and a Torpedo level.