Free Wi-Fi in London.
Londonist is a website all about London, unsurprisingly. Its team of writers highlight news and events, take lovely photos and other such exciting and multifarious activities.
More importantly, from your humble Devil's point of view, Londonist has an extraordinarily useful map of restaurants, hotels, cafés and—most importantly as far as I'm concerned—bars and pubs with free Wi-Fi. As of January 2008, they've got nearly 170 places surveyed: now that's what I call useful information.
The map only gives the name of the establishment and the address—it doesn't tie in with Beer In The Evening, Fancy A Pint or anything like that—but it's a great resource nonetheless...