Here are some websites that may prove to be helpful from time to time.
I will add to this as I find sites I feel are noteworthy.
Here's an online adjective quiz. Great for both 5th and 6th graders.
This is an all-inclusive english/grammar site. I highly recommend everyone to check it out.
This site has some great tips on writing as well as a nice explanation for parts of speech and other grammatical concepts.
I LOVE this site! It is chock full of links to quizzes, grammar reviews and tips, and even a powerpoint presentation reviewing/explaining how to diagram sentences. Parents, do you remember doing that??? I sure do. It's a lost "art form" that might be making a bit of a comeback in our classroom. 
Here's a reading passage with comprehension questions you can answer online (no printing required). The passage is a little dry, but life is full of dry things we need to be able to read and understand.
At the request of several students, here's a website with some games on it. More specifically, this game deals with Egypt.
This website has some more basic reading activities.