to hebui,
There are a tremedous number of outfits that sell prefilled cartridges for Canon printers that take the BCI-3&6 cartridges. Most sell a high enough quality product---in that the ink will not clog the printhead
and will preform every bit as well as OEM ink in that aspect----and at huge savings over OEM ink. Sadly, there area few outfits that make cartridges that will clog printheads or cause problems. So the questiion becomes, how do you tell the difference?---and BTW, price is no predictor. For many, teh answer is printer forums like the nifty stuff forums---just google the name---and there you can find users posting on their experiences with various vendors.
But before I started refilling, I had great results with
www.bulkinkjetcarts.com---in terms of great customer service--with toll free number, very good color balance, and very low prices. To beat Zepper to the punch---he will recommend swiftink which is a quality outfit---but has higher prices. But maybe six months back, there was a 50+ thread on good vendors in this forum---and some of teh recommended ink vendors were troll posts.
But with mail order outfits, you must order in bulk or shipping will eat up the savings.---which can be as high as a savings of 8x over Canon OEM cartridges.---while refill it yourself can offer 15x+ savings.