2021-04-06 NOTE: DC, the guy behind jgram, accidentally let the domain name expire. Someone else rescued it and I think he is planning to revive it himself but the details are still unclear at the moment. I have the most recent copy of the database and will be using it for my daily emails but some of the links will not work.
This is a cool site that offers a database of Japanese grammar entries. Search for a specific (or partial) grammatical point or look at grammar by JLPT level. Also, register and set up your own study lists. Very cool!