What I expect from the Sept 12th Announcement
iPhone (6th generation)
The next iPhone will have a 4inch screen that maintains the same pixel density as the 4 and 4S (640 x 1136). New Apple A6 processor. It will have the new dock connector, and the headphone port will move to the bottom of the device. It will have LTE on Verizon, AT&T, and Sprint. New front facing camera that has the same quality as the back camera on the current iPod touch. The back camera will be slightly better than the iPhone 4S, but not very. Possibly 8 MPs. The branding will be the same as the new iPad, dropping the numbers and letters that denote it's model.
iPod nano (7th generation)
New Retina display of 480 by 480 pixels. Wifi antenna for WiFi syncing, and Airplay. Possibly a new small set of apps (similar to how apps currently work on the Apple TV). Same 8GB and 16GB models, same body design. New dock connector, like all other devices. Longer batter life of around 30 hours. New colors!
iPod classic (7th generation)
WiFi syncing, AirPlay, and VoiceOver, new dock connector. The body of the device will get a little thinner and the headphone jack will be moving to the bottom of the device. Screen goes to Retina with 640 by 480 pixels. Same 160GB hard drive (no solid state for now). Same battery life. New price point of $200. New colors for the iPod classic!
iPod shuffle (5th generation)
The next iPod shuffle will have a memory upgrade to 4GB at the $60 price point and a new low of $30 at the 2GB price point, making it the least expensive iPod ever sold. New colors. That is all.
iPod touch (5th generation)
The next iPod touch will see some pretty major improvements. New 4" display (same as the new iPhone (640 x 1136)). Upgrade to the Apple A5X processor. 16, 32 and 64GB models (dropping the 8GB model for 16GB). Siri. New dock connector. Same back camera as the new iPad. Possibly a 3G version with data plans just like the iPad.
I don't know what the body design will look like, but I hope it'll look similar to the new iPhone, just really really thin.
But there's one more thing...
iPad mini (1st generation)
Here it is! The iPad mini will have the same processor as the 3rd generation iPad (A5X). Same HD front facing camera as the new iPhone. Same back camera as the new iPad. New dock connector, headphone jack at the bottom of the device. I really think that it'll have a 7.85" Retina display. Siri. LTE. 16, 32 and 64GB models. Black and white models.
iOS 6 will be released to the public shortly after the presentation, along with a new version of iTunes (I really want some performance improvements above all else). Perhaps a way to read iBooks on the Mac. I think their might also be a way to see the content from iTunes LPs on the iPad, iPad mini and Apple TV. A new version of cover flow in iTunes where you can click on the album to see all of the songs in that album. Just simple improvements.
The new dock connector will support USB 3.0.
The iPhone 3GS will be discontinued, the iPhone 4 will be $0, the iPhone 4S will be $100 and the new iPhone will start at $200. The iPad 2 will not be discontinued because of the iPad mini as it is really an entirely new product line. All previous iPods will be discontinued and replaced by the new generation.