Crystal Singer by Anne McCaffrey
This series is probably one of my favourites of AM's Science Fiction series..
The far reaching planet colonization of mankind has lead to difficulties in communications and the strange crystal ranges on Ballybran are the only source of a particular crystal, which offer the most effective form of communication available. The series basically follows the life of Killashandra; who leads the prestigious but incredibly dangerous life of a Crystal Singer whose job it is to cut and prepare the crystal for one of it's many uses. (It sounds boring but believe me it's not :)
I really enjoyed the series because it had such a different perspective than many other SF novels I've read. It was very inventive, and each book expanded, and also brought fresh life to the story without the annoying repetition of events which can often occur in a series. (classic example being the Star Wars Trilogy with the Death Star being blown up a second time).. Anyway it's a great series.. I would give it about an 8.5 to a 9 out of 10