Here are some of my suggestions for magic-heavy books :
- Elantris, by Brandon Sanderson (the author who was chosen to finish the Wheel of Time series, btw) : This one is about a city of powerful magic-users that was mysteriously cursed some years before the beginning of the story. The magic system is central to the plot, as some of the main characters try to figure out how it works and what went wrong with it.
- The Runelords series by David Farland : This one has a unique style of magic where people transfers various attributes, like strength and intelligence, to each other. Some of the characters end up really powerful this way.
- The Witches of Eileanan series by Kate Forsyth : There's lot of magic in those books about a world ruled by witches. In fact, in all my suggestions, these are the ones that best matches what you asked for. There's also a sequel series called Rhiannon's Ride, which I also recommend.
The Children of Amarid, as mentionned by Corwin, is a good choice as well, and so is Feist Riftwar novels.
However, while I usually enjoy Weis & Hickman novels, I disliked the Darksword series, especially the last book. It's been a while, so I don't really remember why, just that I hated it.
Funny you mention the Black Jewels trilogy, since I'm actually reading it these days. It's decent, but I don't like it much personnaly. Now half-way into the third and last book, I'm slowly warming up to it, but I don't think I'll read more of Anne Bishop books after this one.