Some exciting news for Kindle owners today! Soon you will be able to borrow ebooks from your local library. Since that was one of the main reasons, though not the only one, that I would not personally consider purchasing a Kindle, I consider that I BIG improvement. I'm not sure when this will happen but the press releases promise sometime this year.
From what I am reading, it is an improvement in the Kindle software that will allow you to read the ebooks already in the libraries' collections and will not require the libraries to purchase additional books. That being the case, even though you can't read them on your Kindle yet, it may be worth checking our your library system to see if the offer ebook lending.
Also check out their specific collection. I have cards to 3 different systems and it is not unusual for find books carried by only one system. You can start building your 'wish list' with most systems, so that once your Kindle is able to download books, you can just go to your wishlist. (As much as I love reading ebooks from the library on my ereader, it definitely is NOT the easiest system to navigate when you are browsing for a good book.)
If there is a particulary popular ebook you would like to check out, you might want to go as far as to put it on your 'hold' or 'reserve' list. Some of the most popular books have a long wait list. One of mine has as many as 20 people ahead of me. Since each can keep it for 2 weeks, that is a wait of about 8 month. If the Kindle is able to use it by the time your name comes up.....GREAT! And if not, you've lost nothing.
You can read more about this new feature for Kindle readers here or here.