Apple's iOS 5 will soon be announced come June 6th at the WWDC 2011 (World Wide Developers Conference)
Steve Jobs will most likely be discussing iOS 5, among other things, at the Keynote presentation, kicking off @ 10AM PST on Monday Morning . For the Hardcore Australian Apple Fans, you'll be able to see the keynote streamed live from Apple's website @ 3AM Tuesday Morning AEST.
So, what's new in iOS 5? We've done some research and found the following new features that are certain to be announced:

Put simply, Apple's iCloud service will be a cloud-enabled music, photo and video streaming service. What does this mean? Basically, once iOS 5 is up and running on devices like the iPhone, iPad & iPod Touch, you'll be able to 'stream' your media from a iCloud server located somewhere, presumably close by to your location. This enables you to have access to your music, photos, videos, and more, from any computer or mobile device you authorize.
Apple have teamed up with the music publishing arms of Universal, Sony & Warner to make this happen - so it's highly likely Apple Store music downloads will be automatically streamed once purchased. There are mentions of being able to put your pre-existing collection on iCloud, but that will not be pushed out until a later date. iCloud could be used for a wide array of applications where data needs to be available across a wide range of devices, and people are speculating that iWork will be one of these Apps put into motion with the release of iOS 5.
The cost of iCloud is said to be free initially, with Apple introducing a $25 Annual Fee going into next year.

Remember Widgets? Mac OSX has had widgets on the dashboard, giving users a space where live updates, feeds and information could be readily accessed in one place. A big rumor for iOS 5 is that Apple will introduce widgets, presumable for use on the home screen. This would be a smart move for Apple considering that Android OS already has this feature.
Right now, the iOS devices don't really tell you much more then the Time, Date, & Missed Calls, until you open / unlock the device. Being able to put widgets on the home screen would be very handy indeed.

Back in April of 2010, Apple purchased personal assistant and voice recognition software 'Siri' for a solid $200 Million dollars.
Siri works by interpreting natural speech and giving results that it thinks would be helpful. For example, if you vocally ask for a nearby pizza restaurant, Siri should (in theory) respond with local listings of Pizza Restaurants.
The Siri iPhone App has been available for quite some time, however obviously if Apple have purchased this software and plan to implement it into iOS 5, it'll become a core function. Hopefully this will replace or improve on the iPhone's current voice recognition functionality, which is lackluster and very inaccurate.

Another strong rumor is that Twitter (& Possibly Facebook) will be embedded deep within the iPhone's OS.
iPhone Users will be able to share photo's taken with the iPhone's camera direct to Twitter.
This one is getting social fans excited, doing away with the need for current Apps to manually Tweet a photo.
There is talk of some kind of Facebook integration, but we have no real details as yet.

This rumored feature of iOS 5 is fairly cut & dry - Apple's new iOS 5 will automatically download Apps as they have updates available, an improvement on the current situation where manual updates much be downloaded via user intervention.
So there you have it, fresh from the Rumor Mill.
Of course, we can't say for certain what will really be in iOS 5, but we're fairly confident that our list will make the grade.