Vocabulary that students don't know or remember how to spell are very beneficial pieces of a word wall. My school's library has a giant white board on one wall that I turned into a word wall. I got these amazing Storybook Alphabet Letters from Shannon Gavin via Scribd! Some hot glue and yes, duct tape, has those bad boys hangin' tough!
I use post-its to write vocabulary that students learn throughout their year in library, then stick it up under the corresponding letter. Vocabulary ranges from bookish terms, such as genre to technology terms, such as website. Through much (pedagogical) thought, I decided there really wasn't a way I could have students write the vocabulary words and put them up. I have too many classes and I don't want to waste post-its.
Having a lot on my plate makes it easy for me to forget simple things like stick a new word on the word wall. I solved this issue by inserting a reminder into the schedules I show the classes. To further publicize the word wall, it is mentioned during the lesson and pointed out.