Buy Instead of an iMac
If you don't need a MacBook of some kind, you only had two real options until today. You could buy a Mac Pro that is due for an update, or you could buy an iMac. The iMac is the more likely option, but it starts at $1,099.
Now you can bring your own monitor(s) keyboard and mouse and avoid spending $300 on a 1080P display that comes with the entry-level iMac. You can get an amazing third-party display for under $200, so this is a nice option instead of buying an iMac.
You also get a lot of power, but unfortunately you don't gain tons of upgradability. You will be able to upgrade the RAM, but it's not clear if you will be able to upgrade any other parts after you buy it.