Are there any later ones you'd particularly recommend? And have you read the other two in the Birthgrave trilogy?
I wouldn't recommend the other two books in the Birthgrave trilogy, since I don't think they are among her best books, either.
As to what to recommend, it depends on what you like, or are in the mood to read -- she writes just about everything! At least in every fantasy sub-genre I can think of, plus a little science fiction, quite a lot of horror (but that's largely vampires), mainstream, YA, and I've probably missed something.
For sword-and-sorcery I'd recommend the
Vis books. For something with a Middle Eastern feel,
The Flat Earth books. For rewriting familiar tales there is
Sung in Shadow (her take on Romeo and Juliet) or "Red as Blood: Tales from the Sister's Grimmer" (fairy tales). For something a little twisted
The Secret Books of Paradys (Volumes I, II, and III -- Volume IV gets too icky for me to recommend it) each book consisting of linked short stories which take place in an alternate fantasy world Paris and spans eras from the Roman to the modern. Or there are her novels set in an alternate Venice,
The Secret Books of Venus, not so twisted, but also spanning a great period of time, from the Medieval to some future date. Or ... well ... a lot of other books that aren't so easy to classify.
Mortals Suns for instance, or the
Lionwolf trilogy.