I'll give my own site a quick plug:
www.roadtogrammar.com
I like to use it with a projector and laptop; it projects well and is colourful and userfriendly.
I also use yahoo answers (
www.answers.yahoo.com) a lot as it is a very natural way for students to interact. Not suitable for kids, though.
I would say though that there is quite a big difference in quality between a lot of the free material out there and the commercialised material.