Try Yesterday's Son and Time For Yesterday, both by AC Crispin - you can't go wrong there (in my opinion).
I just finished "Yesterday's Son." Quite a fun book. STID also got me back into a trek TOS reading mood. What's more, as I was reading "Yesterday's Son" i kept picturing/hearing Pine, Quinto, etc in the roles.
Yes, I am hearing their voices of Shatner and Nimoy