After going through the now cancelled shows I miss in my mind, I decided upon:
Joan of Arcadia, as I'm sure you can imagine is based on the story of Joan of Arc who led the French against the British, because she thought that was what God wanted her to do. In the first episode Joan Giradi, played by Amber Tamblyn is approached by a cute guy professing to be God. Each episode "God", in many different guises, gives Joan a task which normally has unexpected results, such as Joan getting a job in the first episode leading to her paraplegic brother Kevin deciding to take charge of his life and get a job himself.
It wasn't your typical teenage show. It was very intelligent and beautifully written. It had a great cast, which included Becky Wahlstrom, Sprague Grayden and Michael Welch. None of them are exactly household names but they all brought great things to their characters.
The series got cancelled after just 2 seasons and it was a great shame because it had just introduced a game changer brought about by a character played by Wentworth Miller, he of Prison Break fame.