If one were interested in obtaining rare books they can be found on websites such as Abe Books and Bauman Rare Books. If one would want to find them offline they can be found in libraries.
Most larger cities have at least a few locally-owned bookstores, which can be a potential goldmine when it comes to rare books. Some companies such as Bauman Rare Books actually specialize in such items. Larger bookstores like Barnes & Noble sometimes carry rare titles and are worth a try.
By passing everything in the game then you could go and look for some, as in like when you beat the elite four you then could try to look for rare pokemons, or you could get a action replay for ds and use the cheat codes to get rare pokemons.
Collecting rare books is always a good form of investment as any rare item is always valueable in the future. Both new and old books will always have a future value at some stage.
One could find song books for children online at a reasonable price in many different places. Some of these include: Wal-Mart, Amazon, Kijiji and eBay.
You should have the full title & publisher info and do some searches on Abebooks.com, Alibris.com and Ebay.com and see if you can find related or identical books. From your description I cannot really help you.
You could go to the library, and find books about the heart, and its functions. In some of the books you will find pictures of the heart and the diagram of the heart. You could also go to the doctors office they would have a poster of the heart diagram. Those will help you learn more about the heart.
One could find the lyrics to "Not Ready To Make Nice" at lots of lyrics websites including lyrics365 and azlyrics. You can find song lyrics in some music books.
Almost home, all the way home, sliding into home, that's all i could find...
You can find some good nutritious dinner ideas on some diet sites and recipe sites. You could also find some in your recipe books that you have or you can pick some up at the local book store.
There are some great books that contain ballroom dress patterns and could be bought from many online stores. Some of those books are Ballroom Dress Patterns and Misses Sewing Pattern.
I guess probably the earliest Superman comics are the most valuable, but rarest is something different. That means hardest to find. I would guess that some underground or independent books were printed in very small numbers, and so they are very rare.
www.amazon.com