Hi Hampshire Girl,
I think you'll really like their BrainstormIt, if you (like me) aren't/weren't very familiar with SEO. There are other tools that can give you results, but I find their analysis approach to be clarifying (in particular, the supply/demand side of keywords). All that said, I wanted to make sure you (and other folks) knew about the available alternatives:
Mike's Marketing Tools (Official Site)
I think you'll find SBI does stack up pretty well (though a key engine of theirs is still Wordtracker). Internet marketing costs can add up quickly!
I'm thinking of taking some screen shots and posting them here, so people can get a feel for the experience. I'll check with the SBI higher ups to make sure that's kosher first.
Aaron