www.gotbrainy.com is a fun word site where you can upload pictures, choose a word from their list to match the picture, and write a sentence using that word. This is good that they have their own word list otherwise the risk of inappropriate material for school would increase. This site provides a great opportunity for students, as well as adults, to improve vocabulary in a fun interactive way. You also have the opportunity vote on the usage that others have posted as to whether or not they used the word correctly.
The main issue is that students need to create an account in order to contribute. For those of you that are in the elementary realm, this is a genuine concern and I do have some suggestions for you as to how you could use this site. (Also, it is because you cannot upload pictures to this site with an iPod/iPad.)
1. Have one account for the whole class and have students only post on your computer or only use it as a whole class activity. This will allow you to also ensure that the content that your students are submitting is under your approval. Maybe keep the word list available, have students look up the words, and think about pictures they could take to match the word prior to posting.
2. Only read examples and use it for voting purposes. It would a fun activity for the class or a group of students to make decisions as to whether or not the author is using the word correctly. This would eliminate the need for an account altogether.
3. Have students do a similar activity using an app like Doodle Buddy. Then the students could have a picture, vocabulary word, and the sentence matching the picture. This would avoid the issues of students having accounts, but yet they are still integrating technology into their vocabulary study.