This is great value - these Mifi units take standard SIM cards and then act as a router so you can connect to them from several other devices. This is a great way to get internet when you're out and about on a tablet that doesn't have 3g. You can connect up to 8 devices to it at once (I think??).

This comes locked to T-Mobile but you can unlock them easily, with codes available on the net for free, or for 99p on eBay if you can't be bothered to search around too much. Once unlocked you can put any network's SIM in them, which makes them perfect for Samba mobile internet SIMs (see post about Samba here if you don't already know about it) so you can get free wifi wherever you happen to be. These Mifi units are about £40 from Amazon (albeit unlocked ones but as they're so easy to unlock this offer is much better value) and are usually £30 from Tesco but currently reduced to £25.