the class is an hour long and i need to occupy half of the class while the other half is testing. does anyone have any ideas for a silent, independent activity related to language arts?

Independent research report on a student-selected topic of interest, or have the students create their own poem or short story anthology. Another fun thing for the students to do is to create lessons or books for younger students.

Every time I need to keep a part of my class quiet and occupied I do a word search with vocabulary or spelling words. Its really pretty cool, check it out:
www.puzzlemaker.com

Yuck. That's a tough one, considering that it's 8th grade, and a lot depends on what they are studying. Back when I taught, I had a fair amount of success with things like giving them a short poem to illustrate or having them write a letter to a famous person. I'd suggest that you have more than one activity on hand so that they can have a choice, and I'd suggest that you make those activities appealing to a wide variety of different learners (such as the two acitivities I suggested would appeal to two different learning styles.)