Computing consumables such as original and compatible inks, paper, memory sticks, pen drives, compact flash, SD and other memory cards; CDs, DVDs and other storage.
Branded and compatible inkjet cartridges and ink refills. Also CDR/DVD media, photo papers and other computer consumables. Free UK delivery
Cartridge Monkey. Mainly original and remanufactured ink products. Also sell paper, labels and transparency film. Free UK delivery on all orders
Printers and CD labelling as well as original and compatible inks. Free UK delivery.
One free cartridge for new customers with most Canon & Epson inks. Free photo paper with HP & Lexmark. £2.99 delivery charge per order. 
Original & compatible inks, paper etc. Double capacity cartridges and buy 1 get 1 free on most compatibles. Free delivery over £10.
Sell original and compatible inks. Good prices but not easy to find the cartridge you need if you don't know the code. Free delivery over £15 otherwise £1.
Internet Ink make and sell printer ink. Free delivery on all orders and 10% off repeat orders.
Better known for cameras, also sell ink and paper. You can reserve online & collect from shop. Free UK delivery over £150, otherwise usually £3.95.
Lots of components and other electronic gadgets as well as laptop batteries, discs and memory. Free delivery over £35, otherwise £2.99.
Specialise in memory cards but also sell other peripherals. Good prices and free UK delivery on printer ink, £3.95 on everything else.
Good range but not much depth. e.g. ink for only some makes of printer, but sell other stuff. Standard UK delivery from £2.50: free on ink. 
More difficult to find the ink you want unless you know the code. Good for discs. Free delivery.
Not usually the best prices on original manufacturers inks but 'buy 2 get 1 free' and other deals on some compatibles and remanufactures make them worth a look. Free delivery.
Other branded inks at huge discounts
£29.99
See also ...
Many of the shops on the Stationery page also sell printer ink and other computer sundries at good prices. In particular, try Euroffice who offer 20% discount if it is your first order with them.
A separate page has suppliers of computers and computer peripherals. On this page we guide you to suppliers of printer ink, DVD and CD blank discs, memory cards, flash drives and other computer and printer sundries.
Comparison of ink prices is quite difficult because postage can make up a large part of the total cost. If you do only want one or a few cartridges, companies that offer free postage, such as Internet Ink will normally turn out to be the cheapest overall, even if their individual cartridge prices a little more.
Also, look out for the freebies. For example, inkClub give a free cartridge to new customers ordering Epson or Canon compatible inks (but they charge £2.99 postage on all orders). Internet Ink offer a 10% discount on subsequent orders once you have made a purchase.
For printer ink, it is worth checking inkfactory for good overall deals, allowing for offers and postage. In many cases they sell double capacity cartridges and there are also buy-one-get-one-free offers. If you are lucky, the ink you need may have a double capacity cartridge and a BOGOF, giving you four times the ink for the price of a single cartridge, and free delivery if your order is over £10.
The inkXpress web site looks very old-fashioned and is not very user friendly. It is quite difficult to find the ink you need if you only know the printer model rather than the cartridge code. But if you want original ink, rather than compatible ink, it is worth making the effort as they have some of the best prices and frequent discount codes - published on their own web site - which reduce the cost further, typically by another 10%.
Although Play.com are better known for music and pre-recorded DVDs, they have a good selection of branded blank CDs and DVDs at very good prices with free delivery on everything.
MyMemory are usually the best for flash drives and memory cards. Their own branded drives and memory cards are particularly inexpensive, but branded ones, too, including the Sandisk Cruzer range, are excellent value.