The 3.0 FRCS has the Shadow Adept, and IIRC it is very powerful but also holds many prerequisites. However it has a strong connection to the setting, being a devout follower of Shar and having abilities related to the shadow weave, so it may not necessarily fit in your campaign.
I am sure this is not what you're looking for, but I played a shadow wizard in early 3.0 days, I only used PHB material, and I just altered the description of all my spells so that they had a shadowy appearance (without changing the mechanics).