I totally understand wanting to save your important information before wiping your device! If I can find out what you need to save, that would help a lot, however, I will do my best to assist here.
The memory card on the phone carries a lot of the information. I am not sure if you were going to sell that as well, but I might recommend simply plugging the card into an adapter (USB or a larger memory card adapter) and then into a computer to see what files (photos, music, ect) was on there that you should save. Then after you have saved everything format (erase) it with the rest of the device and you are all set!
In terms of your applications, that information should be saved through Google and if you get another android device, you can simply redownload the apps on to it.
In terms of text messages, I would suggest sending the ones that you need to your e-mail (same thing as sending a text, just put your e-mail in the TO field). You can also find 3rd party apps that will save your texts for you.
If there was any other information that you needed to save, please let us know!