I Googled around and found mixed reviews on 4inkjets. I wouldn't use them.
As a buyer I would want to know what mfr's product they are selling.
For example, from my experience, I would stay away from OA100 brand generic cartridges.
OTOH, TrueStar brand has been very satisfactory in a friend's Canon MP600.
I am a refiller, but if I were to buy refilled, non-OEM (generic) cartridges, it would be from one of the following vendors :
Jflan is correct. The Truestar carts work best. They actually are genuine remanufactured Canon cartridges, but that might change shortly.
Whatever you do, do not use the PRINT-RITE brand of PGI-5s and cli-8s. The contacts on the printer do not line up with the incorrect chip placement on the cartridges. I just purchased 49 of them for customers; all had to be returned.