Harpers books are very hit or miss. Go with any of the Elaine Cunningham ones though. Nightparade is particularly awful--can't stand that writer: skip anything by him.
Icewind Dale and Drow Trilogy are good.
Moonshae trilogy is decent.
Wyvernspur trilogy is excellent.
Some of the Ravenloft books are good, but again, hit or miss.
Cleric Quintet was pretty good (though some of the "twists" were unforgivably obvious).
SpellFire was good.
Somewhere around there I lost interest--I think it was about the 8th book about the Icewind Dale characters.
Avatar set was troubled by the fact it was written by three different people using the same pseudonym, and one of them sucks (I think the one who wrote "Night Parade" was the guilty party).