Hi Janine
Have you looked at Quest Central (http://www.quest.com/quest_central/qco/performance_diagnostics/)?
It has a whole bunch of stuff that includes performance diagnostics. Once it's installed, you tell it to monitor performance, and it looks at hi-load / badly performing queries, and makes suggestions about how to improve them, including additional indexes.
You can get a free trial version, so see what you think.
<Raad>
