These sites below helped us a great deal and we're sharing how we used these sites. We don't know yet if we're doing it right but we'll update you as we see results. These sites were recommended to us by the above people in the know at The Selling Lounge.
Use the first to help with the most popular keywords for your item. If you're revising a listing, you can plug the item url into the box and you'll get a whole list of keywords. Compare those to your original keyword choices. If you are working on a brand new listing type in your item and see what comes up. Word your description around the best keywords. In either case, choose which are best for your item and write your description around them. Make sure they are relevant keywords!
Google Keyword Tool
We used this second site to fine tune our meta descriptions and keywords. This one tells you the exact number of characters and keywords that are "robot" friendly. It also grades your keyword, title, and description relevancy. These concepts are hard to explain and the best advise is to learn as you go. You'll soon get the hang of how these three things relate to each other.
SEO Centro meta tag analyzer
We also came across this next site a week or so ago. It shows where your item is placed in the major search engines based on your keyword phrases. We still have a lot of work to do but this tool has shown some improvement in ranking for some of our listings. Any sign of improvement keeps us focused and motivates us to continue working on keywords, meta tags and SEO, OH MY!
Mike's Marketing Tools
Good Luck!
Tip:
Don't put your shipping info at the beginning. I've always done this because many buyers don't read to the end but apparently this is all wrong if you want your items to be found in search. Search engines read only so much of the listing and they start at the beginning. If your shipping info or any info other than your item description is at the top, chances are your item will not be placed well in searches.
Share with us any SEO tips you may have picked up along the way. If you've used the above sites let us know if you found them to be helpful. Share your numbers with us and keep us motivated!