Recently bought myself the wonderful Moto G 4G and bought myself a 3 Pay Monthly sim to make the most of it.
Was torn between the Essential Internet 600 SIM 12mth (600 mins, 5000 texts, 1gb data) for £9.90 and the more expensive Ultimate Internet 600 SIM 12mth (600 mins, 5000 texts, AYCE data) for £15.90, ultimately going with the cheaper one because hey, less money.
After looking around the 3 account, you can buy add ons, one of them all you can eat data for an extra £3 a month, meaning you get the same at the Ultimate Internet package for £3 cheaper than it should be.
TL:DR - Essential Internet 600 SIM at £9.90 + £3 AYCE add on = cheap contract.
edit: I only found the add-on when I'd signed up and looked around My3 account, you can't add it when you're buying the sim online.
edit 2: http://tinypic.com/r/2zxuxb6/8
For those of you wondering if such a mystical and wonderful deal really could be true. I'd post a photo of a bill but I don't have one.
No tethering allowed on this plan.