Given every man and his dog has already covered this evening (and I've been travelling all day) I'll point you to Apple's webpages and give you a very brief summary.
iMac - Basically the big news is that there's a new version, to go alongside the slightly upgraded standard versions, which has a 5k display. That's 5k, not 4k. The painful bit is that the new 27" retina screen costs an extra £400 than the standard 27" version, meaning it will cost £2k (see what I did there! ) for the 'basic' model. As a side note, there's no dedicated 5k display for Mac Pro users.....
Mac mini - There's been a minor spec bump with more power and better connectivity, and they've dropped the price slightly too by £100. Not bad really if you're looking for a desktop.
Whilst we're talking macs, it's worth mentioning that Yosemite should be available to download by now as a free upgrade. As much as I want to download it, and using it's handover with iOS8, I won't until all the bugs become apparent. I'm starting to treat Apple like I used to treat Microsoft and wait for the first major update. Shame on you Apple.
iPad mini 3 - It's basically the same as the iPad mini 2, but has a Touch ID sensor, and is also available in gold. That's it, really. Nothing else. Apple will continue to sell the mini 2 and original mini, but will drop prices. The iPad mini 2 looks like a bit of a bargain compared to the mini 3 unless you really want that touch ID (but the biggest size is now 32GB....)
iPad Air 2 - Strangely, this excites me. It's got a new A8x processor (supposedly better than the iPhone 6's A8), an improved 8MP rear camera knicked out of the iPhone 6 (no OIS), and it's super skinny. I mean it's skinnier than the iPhone 6. It's also got the same styling of screen as the iPhone 6, and I'm preying they've changed the screen glass compared to the original Air, which felt a bit meh. Of course it's also got Touch ID and improved wifi connectivity.
Other things worth noting, battery life remains the same on the iPads, but the Cellular versions of the iPad Air 2 and iPad mini 3 also include an Apple SIM. What's that? Well, it's a sim which lets you add temp data packages on it from different networks. Only EE is an option in the UK, but it's also got a couple of US networks as options, and you can bet other networks around the world will be added. This could be really interesting for international travellers, and it's significant as all networks had been fighting against such an idea in the iPhone. So watch this space!
Whilst Touch ID isn't the end all and be all. Having used it on an iPhone 6 now for a couple of weeks, I'm finding it really useful as lock, and also to activate certain features in some apps. Where I think this could have a significant effect though is in business. When paired with the partnership with IBM, I can see a lot of businesses getting excited by this, for different security and user profile purposes.
Another thing worth noting, I'm now lusting for a 4K display for my desktop now....