SpellingCity w/out a doubt is my favorite site for Spelling and Vocabulary. This is a great site w/ educational portal that allows educators to create word lists that can be incorporated into educational games. These games are not only fun but highly engaging and help students learn their "words". Also, an educator can track students, find an abundance of resources/videos, and even use it for mobile learning w/ a free mobile app (iOS/Android).
I highly recommend checking out SpellingCity by clicking here!!!
Below is a brief demo of the free mobile app...
*SpellingCity is an advertiser of Technology Tidbits.