I almost always keep a tab open to SpanishDict.com and another to Google Translate while I am working on a lesson. So if I find a word I don't know, or I don't understand what the conjugation used is doing, I pop over to SD and research it. Other times when I am working on sentences or phrases the one used, or the one I am trying to use, doesn't comport with RS. So I will paste the sentence into Google Translate and see what it does with it. You have to be careful of all machine translators but I find it will often at least point me in the right direction.
From other students here I learned of the great little book, English Grammar for Students of Spanish by Emily Spinelli of the University of Michigan (Go Blue!). It explains the grammar very well and has sample sentences.
I have also used the web site drlemon.com for grammar.
I still recall working through the first course and suddenly noticing "está, ésta and esta" and wondering if it was a typo. After a lot of independent study I figured out the differences. It seemed very frustrating at the time, but I believe that the time I spent researching it on my own taught me how to recognize and use the words in a way I will never forget.
Oh, I almost forgot the best resource you have: others of us in the forum. Just ask your burning grammar questions here and see how fast they get answered! Ricardo and Esteben have this stuff down cold, and others of us can help as well.