Cassandra Palmer Series

The time traveling, ghost-whispering, crazy blond who started it all currently has six books in her series: Touch the Dark, Claimed by Shadow, Embrace the Night, Curse the Dawn, Hunt the Moon and Tempt the Stars. They follow each other in chronological order (or as much as possible with Cassie's tendency to time shift.) They are best read in order, but stand alone reasonably well. They tie in with and overlap the Dorina Basarab series, which is set in the same universe.