ACE centre produced a great website tool to enable you to compare different aids - all major aids are listed.
It gives you a summary overview of each aid, photo, cost and where to purchase from.
A good site to use in school when explaining different aids.
http://www.speechbubble.org.uk/
SERC / Newbridge School
Barley Lane Campus, 258 Barley Lane
Goodmayes
Ilford, IG3 8XS
SERC is a service and information centre brought to you by Redbridge.