Apple is hosting a special media event tomorrow in San Francisco, and we’d thought we’d give a cheat sheet as to what to expect from Steve & Co. Don’t be surprised to feel a sudden urge to whip out your credit card in just a few hours.

For the past few years Apple has used an event in September to announce new iPods and iTunes-related items. The company has sent out this rather obvious e-mail (pictured at right) to various media, which all but confirms that we’ll see something music-related tomorrow. Furthermore, we’ve been seeing supposed shots of the new iPod nano, along with matching protective cases.

So if we had to guess, we’d say to be on the lookout for new iPod nano tomorrow. Bigger screen, more memory, etc. The iPod line itself may well see an across-the-board price cut, too, to better differentiate it from the iPhone. (The iPhone could be getting a new firmware version, too, bringing improved GPS reception.)

There’s also rumblings that iTunes will see a pretty significant update, bringing the software to version 8.0. “Rumblings” meaning selective leaks from Kevin Rose, the former TechTV host and founder of Digg. We could be looking at a rather cool new visualization called Magnetosphere, seen below.

Magnetosphere revisited (audio by Tosca) from flight404 on Vimeo.

The other big iTunes 8 rumor is a new Pandora Radio-like playlist suggestion feature called Genius. It supposedly goes through your music library to create recommended playlists based on things like song rating, play count, etc.

Of course, we’ll have an update as soon as Apple reveals the goods.