Is there a way for me to transfer music from my iPod to my iTunes? Say, if I accidentally deleted some music on my computer but I have the files on my iPod?
Putting your iPod in Disk mode will work for iPods other than the iPod Touch. For the iPod Touch and iPhone, you'll need to use a tool that is capable of reading the iPod Touch/iPhone database.
One such tool is MediaMonkey -- the free version can handle this. Here are the instructions.
Disclosure: I work on MediaMonkey, but happen to feel that it's the best tool for the job.
On Windows, you can use iDump to extract songs from the iPod then throw them into iTunes.
This program will allow you transfer your songs from your iPod to a PC, iDump does come wrapped in installer but you can simply drop the .exe in the root directory on your iPod and run it from there.
On OS X there is expod:
expod is a small utility for getting songs off your iPod. iTunes does a fantastic job of copying music onto an iPod, but lacks the ability to go the other way. With expod you can copy any or all of your songs (or videos) off your iPod, using whatever file naming convention you like.
… and podUp, both free as well:
podUp is an application which copies all your music files from your iPod to a folder of your choosing, without having anything to do with iTunes.
For the Mac there's a shareware app called Senuti that probably does exactly the same thing as the free apps, but has nice instructional videos on the web site, and possibly a more Appleish user interface.