The Texas Language Technology Center of the University of Texas has a very nice online grammar of German, .
A snippet from their about page:
Welcome to , an irreverent revival and shameless exploitation of 19th-century Grimm Fairy Tales for honorable pedagogical purposes. Fortunately for you, Dear Reader, thirty-six from these fairy tales have returned to 21st century Germany (their precise location cannot be revealed for privacy reasons) to model all things … anything the most eager language learner may wish to know about the German language. … This online grammar reference was created for lower-division language courses at the , but any beginning or intermediate learner of German may use it completely free of charge, as long as he or she is willing to take a trip to the imaginary world of Grimm Grammar … the characters of which are grumpy and gorgeous, scary and smarmy, witty and wicked!
If you’re getting started in German, check it out; you could probably skip the introductory German grammar book, and instead just wait until you need a copy .