There's a really good thread with recommendations on books for PM&R. I thought it was a stickie, but unfortunately it doesn't seem to be...
Everyone seems to recommend PM&R secrets. Personally I didn't like it. I found Coopers Essentials of Physical Medicine and Rehabilitaiton much better. Check out Amazon/google books to get a preview to see if either might fit your style. Ross's Chronic Disease and Disability is really good as well, but a little dated.
There are some good SCI or TBI specific pocket books that I found useful for SCI and TBI specific rotations/weeks. I think they're both by Nesathurai. They're not the most recent, but they really hit the main topics and is easy to carry in your pocket, unlike the other texts I mentioned (Pocketpedia is, but it's not in essay format likes these are). I liked them for my week on SCI and week on TBI.
PM&R Pocketpedia is a must. I think the older edition (the black one) is far better organized. The new one is much bigger/thicker, but mostly because they made the font bigger. They did add some more peds stuff, but the innervation tables are buried in the text and harder to reference.
Honestly all you probably need are Pocketpedia, and some good intro-level text (Secrets, Essentials, etc.). I mostly used the Pocketpedia and Cooper, though I actually got Braddom at a really good price. Honestly, I referenced it much less.
Also--don't forget a good, heavy, reflex hammer!
I hope you enjoy your rotation and decide to pursue residency in it.