Re: One word...
I've found Tesco Mobile to be very good as well.
Sits on the O2 network, so great in London & South East and since last year (at least) they advertise the phones and bundles separately, it's still on a contract though, but the only issue I've had with them is their refusal to deliver a handset to a work address.
So you pick your phone, pick your tariff, decide how long you want the contract to be and that's it. Once you've paid for the phone it reverts to the tariff price
I've also been impressed by the fact I've never gotten upgrade nags or upsell from them, well once when I upgraded my data plan "Our records say you have phone X, would you like to look at the available handsets" and they took 'No thanks' for an answer and didn't try to sell me more data\minutes\texts.