Look around for a continuous ink system (CIS). Make sure you buy a good one with high quality ink, otherwise these will damage your printer. Check the warranty on the website before you buy. If they don't give a lengthy warranty and a satisfaction guaranteed - don't buy from there.
The new Iris system works for many HP printers and soon they will be compatible with many Brother and Canon inkjet printers as well.
I don't like needles or open ink bottles lying around so i would pick one that doesn't require them.
Good luck in your search.