Bahah! I know Yuki knows about Kim Harrison, and I was meaning to check her out sooner or later. I downloaded a CRAPLOAD of ebooks and I know I have both of their stuff.
In vein of 'related series' I'll bring up anything by Karen Marie Moning. Her stuff is awesome, and ACTUALLY manages to get better and better each time. For example a review of an audio version of a book from her first book in the fever series:
*reads*Originally Posted by Amazon
Okay LOL I am completely shocked that I saw the LKH was mentioned in that review. Whoever wrote that is wrong because there is no sex in that particular book, though Moning is a master of erotica (better than LKH). Anyway, guess I'm not the only one who thinks the novels are sort of on the same vein. XD If you decide on reading Karen Marie Moning, I suggest you start at Kiss of the Highlander and then go~
5. The Dark Highlander (2002) - One of the best
6. The Immortal Highlander (2004)
7. Spell of the Highlander (2005)
Fever Series
1. Darkfever (Oct. 2006)
2. Bloodfever (Oct. 2007) - One of the best
3. Faefever (2008) - Comes out the day after my birthday <333333
~I hear the ones before that are awesome, but they are only loosely related. Everything gets tied together from Kiss on. Each novel is narrated by a separate female protagonist, with completeeeely different stories in chronological order, but live in the same world so the stories are tied. In the fever series, which is reviewed above, it is from the point of view of the same person, and consecutive in story though in the same universe as the previous novels if that makes sense lol.