I recently finished the three most recent Janet Evanovich books/Stephanie Plum Series (Sizzling Sixteen, Smokin' Seventeen and Explosive Eighteen). I really enjoy hearing these read. I find the dialogue even funnier when narrated by Lorelei King, I enjoy all her characterizations.
I also am making my way through all the Robert B. Parker Spenser series in audio and I have enjoyed both narrators I have heard so far. I have discovered I like these books better if I don't read them back to back but read something else in between.
I also just finished the Sue Grafton book V is for Vengeance. Having read all of Grafton's other books on paper, it was enjoyable to hear it although I could go either way for this series (paper/ebook or audio).