I found
this fabulous little Keyword Density tool to help you analyze the keyword density on any page of your site - simply fill in the blanks and let it run a report for you - will suggest phrases for improvement as well as analyze page titles, descriptions, etc.
We talk alot about optimization here but it can be difficult to really find the optimal *density* of keywords in your content (text) - this tool will help you determine where you're at and how you might improve.
P.S. 6-8% is considered optimum for "natural" language text (ie - not spammy text) but there are some sites successfully working up to 30% keyword density - it takes careful articulation of your content but has been done.
Keyword density = the percentage of times your keywords appear in the text of any given page relative to the rest of the (non-keyword) text.
Remember: it is always better to err on the side of your reader/visitor than to try to optimize the heck out of your content. Super dense pages aren't going to do you any good if you're turning up for high search results but the clients can't get through the
SEO-gobbledy-muck of your text
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UPDATE:
Thanks to Debs5 for finding a new tool that works (apparently the tool listed above is no longer on line)
Here's Debs' follow up:
If this one isn't working anymore, you might find this helpful Hubspot Website Grader. I ran it and have been making improvements on my site with their suggestions. I've been finding Hubspot to be very useful the past few weeks. They also have some awesome free webinars in their archives that you might like in regards to marketing and SEO you can find them here.