One that I started this summer and read in between studying, was the classic seerah - The Sealed Nectar
- I have a little bit left, so when I get home next month, insha'allah, will finish it up.
I just ordered al-Ghazali's Duties of Brotherhood
, after Br. lucid said it was amazing.
Others I've read:
1.The Karen Armstrong biography that you mention Sr. Christine
2. Martin Lings' Muhammad: From the Earliest Sources
I have to admit, I haven't read a lot of the classic Islamic authors, so that is something I want to work on in whatever time I have left.