Felicia Day's Vaginal Fantasy book club introduced me to Meljean Brook's Iron Seas series, which is a fun steam punk romance with really cool stuff and interesting characters. The women are capable, competent, and ambitious (see how I broke free from alliteration?) and the men are interesting and not usually annoying. That seems like faint praise to anyone who hasn't read a lot of romances, but it's really not.
Heart of Steel spends most of its time on the cool ships and zombie-fighting techniques, with excusions into nifty snatches of backstory for the adventurer hero and the pirate heroine, and gives just enough romance (and sex) to hold its head up in its marketing category. It was a fun read.
Yasmeen, the main character, is Asian, and the cast is very multicultural, so I think it qualifies as a Diverse Book for the Challenge.