This nice SEO tool allows you to check your rankings for up to 5 keywords per day for FREE and it keeps an archive for you. All you need is to sign up for a free SEOmoz account. The coolest part is that you are able to download your archived rankings as CSV.
When you install the “browser button” it automatically copies the URL of the page that you are visiting into the tool for a fast ranking check. Since this free tool can handle up to 5 keywords daily, you’ll be able to check approximately 150 keywords monthly.