Examples

http://www.bbc.co.uk/schools/ks2bitesize/english/spelling_grammar/spelling/play.shtml

This is a game where prefixes are added to words and the person playing has to find a prefix that works with the given word.
The game helps not only in enhancement but also effectiveness. I teachs an important rule of building words and discovering their meanings, while at the same time it is a fun and engaging way for the students to learn.

http://www.funbrain.com/cgi-bin/sc.cgi

The game is a spelling game in which it asks you to pick which of 4 words is misspelled and then spell it correctly.
It is very effective way of getting students to memorize spelling tricks like "i before e except after c" It is also efficient because it is in a format that is almost like a fun drill.