If you are going to buy a SD card here is a little tech for you.
1) There are actually two types of Secure Digital (SD) cards: SD and SDHC. SD cards cary in size and go up as high as 1gb only, SDHC the HC stands for High Capacity starts at 2gb and goes on from there. To be able to use the SDHC your device must be able to read the HC format which is different from the SD format. I am pretty certain that all readers can handle HC, but its worth checking.
2) Class referrs to the speed of the card rather than the size of it. The higher the class number the faster the card is. You will find that the higher capacity cards, not only cost more but have lower classes, in other words are slower so you need to find a happy medium between size and speed.
For you I would recommend a 16gb SDHC. Half of the caqrd would go to your MP3s and still have half left over for your ebooks and you do not trade away much in terms of speed. Looks like the best deal for you is Mwave for $16 http://stores.nextag.com/store/47689...shot-sdhc-card