My favourite Star Trek books are the New Frontier books and the one of those I enjoyed the most was Double or Nothing (Double Helix 5). Seeing Riker trying to lead that crew was priceless!
As for screen-related tie-ins my favourite is the novelisation of The Wrath of Kahn by Vonda McIntyre. It adds another diminsion and I love the extra stuff with the scientists you barely see in the film. I even named my computer after Delwin March. (Yes, I'm that big a nerd).
I also rather enjoyed Ice Trap. Lots of Uhura and Chechov. What can I say. My trinity is Chechov, Sulu and Uhura.