Smarthinking is a reputable tutoring service provider. I use their services for courses in Algebra through advanced math (linear algebra, single/multivariate calculus, etc.) and the students seem to like the services. Smarthinking is free for students enrolled in our intermediate to advanced math courses.

http://smarthinking.com/

Daa'iyah Na'im
Director/Head of School
The AGVI Academy for Gifted Youth
http://AGVIgifted.org