While Valve sells its own collection of Portal 2 merchandise, nerd internet store Think Geek is doing its own bit for science, first with testing gel and now with these classy posters based on the hit first-person puzzler.

While Valve's prices tend to drift towards the "fancy" end of the market, these are highly affordable, as you get a pack of four posters for just $15. Three of them measure 18" x 24, while the collage of 40's signs comes in at 24" x 36".

Portal 2 Underground Poster Kit [Think Geek, via Wonderland]