I am using too the Tae Kim grammar guide (wich is free),it properly explains the grammar,and I also review the grammar points on the site japanesepod101.com wich has thousands of funny podcast/audio lessons,every lesson cover specifically one grammar point,but since it comes with a dialogue to display that grammar point (wich is read 3 times,normal,slowly,with english translation) and the .pdf ,you get to review so much more in every single lessons and constanly practicing all the grammar that you learn :)
That is not free though,but you get all of that (access to all the audio and video files + pdf) with the basic subscription that is fairly cheap :)
Only 2 things I don't like about that site is that they are focused too much on making money,in fact at the end of every podcast (wich usually last from 15 to 20 min) they waste 2-3 minutes of your time publicizing their site and telling you to upgrade to premium user,wich is fairly annoying since you ear that even if you just paid your subscription, and soon you'll see that as audio spam,also they have this fishy approach toward the subscription,for example,if you watch the subscription upgrade page you will see the Basic subscription is only 4$,but once you click on it and you are writing down credit card informations, you'll find that is 4$ only if you subscrive for 24 months, and 8$ if you want the basic only for 1 month...so a really fishy approach,wich in my opinion is not suitable to that site,since what they offer is still a lot of good study material. If you can watch beyond that,it is worth to subscribe :)