I was also going to suggest heading to Upper Krust's site.
I particularly like where he takes the definitions of Heroic, Paragon and Epic Tiers and proposes changing the levels of monsters to actual match those definitions. This is a great starting point for thinking about Epic design because it makes you stop and think, "What is an Epic threat?" I think one of the things that 4E got wrong was making things like swordwings - basically an upper Heroic monster - into an Epic monster despite the fact that it does not pose the sort of threat that Epic should actually be about.
I like the idea of Swordwings for my Forgotten Realms campaign - I just bought 3 Swordwing minis

For a different setting I would go with the 'Epic Threat = Destroyer of Worlds' type stuff ok.