Duden make good solid dictionaries. But they've also got a great project going on for "scene languages", in the form of a wiki - not unlike the English-language Urban Dictionary (which can be a very useful resource for translating, and is always entertaining). The Szenesprachenwiki is beautifully presented and chock-full of exciting German neologisms in various categories - the worlds of work, technology and computer games being the most linguistically productive.
Let's take a closer look, shall we? The latest entry at this very moment is "paniert" - defined as the mental state after smoking a joint and presumably derived from the adjective literally meaning "coated in breadcrumbs" and the term "panne" meaning "broken down" as applied to crashed-out bodies. Or we have a useful anglicism, "Drailing", meaning the sending of drunken emails. Or how about "Fernverkehr" for telephone sex - reminiscent of that delightful term "Münzfernsprechgerät" or payphone.
On the whole it's a great site and a good response to fast-moving language development. I find it better than printed slang dictionaries, which tend to be cringe-makingly outdated before they even hit the shops. Aside from a few strictly German phenomena such as "Bionadebourgeoisie", many of the terms seem to be fairly straight loans from English: graduaten, benchen, Chartstürmer, Styler, etc. etc. But they do tend to be used with a pinch of salt.
There will apparently be a printed version of the dictionary out in the autumn, crediting all the contributors. Wie opfer.