Arcademics
Arcademics: Word Invasion
Practice parts of speech by zapping "jellyfish" words that match the word type provided. Students can select the part(s) of speech they want the game to focus on, as well as the level of difficulty and speed of the game.
Other
Using english.com: English Grammar Quizzes & Worksheets
A nice treasure trove of printable grammar worksheets organized by proficiency level: beginner, intermediate, and advanced. Emphasis is on parts of speech but you'll also find some that focus on common spelling issues and vocabulary...
Other
English Forum: English Language Quizzes and Exercises
Grammar, vocabulary, and spelling quizzes and practice exercises designed for students learning English as a second language. Activities are interactive, and users receive immediate feedback.