Best iPad/iPhone apps for someone who's visiting London UK?

What are the best apps? I see plenty and most charge for the app but I don't wanna buy random apps if they suck.
Also, there's tourist apps but there isn't a specific London visitors section on the iTunes store lol.

Please let me know which are good for the tubes, attractions, happenings etc. And if you've used them yourself.

You can visit edenpod website or visit this page
http://itunes.apple.com/...03464?mt=8