Perplex City is a combination ARG/puzzle game.
The ARG part spirals all over the Internet, and involves a hunt for a sacred cube stolen from some aliens, who've recruited puzzle-loving Earth residents to help them out. There's clues on the puzzle cards, but most of the clues are on the various websites and blogs and at live events they hold occasionally (they seem to be based in the UK, so UK players have a bit of an advantage there). There's a prize of £100,000 pounds, or US$200,000, for finding the cube.
The puzzle part involves cards, which you buy (my local EB stocks them) and have puzzles on them. They range from red puzzles, which are common and easy (things like 'what number is 3.14159265...) and go up to silver, which is super-rare (my hardest card is a purple card, which involves computer game cheat codes). You only get six in a pack (the packs cost about £2.50 each, so about $5 or $6 US) but they're good quality, with good artwork and the puzzles inside would give you about an hour's worth of entertainment.
You can also put tags on your profile, so you can see how many other players play, for example, 'DROD' (as it is, there's one. Me.) We'd better get that up some.
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What do you call an elephant at the North Pole?
Click here to view the secret text
×Lost.