If you use FeedBurner to deliver your RSS feed then you’ll want to check out Feed Analysis by BlogPerfume. Plug in your FeedBurner URL and Feed Analysis will spit out a variety of pretty charts of your site’s RSS activity.
Whereas FeedBurner only provides reports for the last 30 days, Feed Analysis will report your subscriber count, number of daily views and clicks for up to 50 months.
Don’t forget to mouse over the charts as they are interactive.
It will also predict the number of subscribers you will have in the next 3,6, and 12 months which could be useful if you’ve actually set some goals around these numbers.