The situation has changed since this question was first asked in 2012. There is now an OFL-licensed, completely version of DIN called. This is legal because DIN 1451 is a product of the German government and is so in the public domain, only the individual interpretations of it by various font foundries are protected and copyrighted.
DIN Next Pro Condensed Bold Font: DIN has always been the typeface you root for—the one you wanted to use but just couldn’t bring yourself to because it. Larabie Fonts is able to offer unique free fonts through the generous support of visitors to the site. Making fonts is my full-time job and every donation, in any amount, enables me to continue running the site and creating new fonts.
Din Condensed Bold
Thankfully Peter Weigel traced it for us!:) Original answer: I don't know how close you need to come to the DIN typeface, but I found a couple possibles on Google Web Fonts. Using the letters aGgQqlJ to narrow down the letter shape matches, I found: Wire One - The lowercase letter shapes are quite similar. The overall font is a bit more more condensed than DIN and some of the capital letter shapes are different.
Abel - Also, not an exact match but the feel is quite similar. If you have access to Windows fonts, the recently announced looks to be Microsoft's interpretation of the DIN outlines. In some time it will be available on many computers running Windows and could well be a good, free and close representation of what paid DIN fonts offer. Our new first OpenType Variable Font Bahnschrift is now included in builds. This new font industry standard enables us to pack an entire typeface family into a single file with infinite variability.
No longer are you constrained to simple weights like Light, Regular, and Bold. Now you can have an infinite range of font styles, with smooth interpolation from Light to Bold and beyond. Better still: because a single, efficient variable font can replace several static fonts, variable fonts save a lot of space.
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