I thought I would share a little houserule and game mechanic I've used in my C&C games (which can be applied to any D&D type game). I've been using this successfully for the past three years and was something I was going include as an option in the Ballista.
Now, it the concept behind the mechanic isn't entirely new and it's been seen before in other applications. It also looks like D&D Next may be using something like it as well. The mechanic in question has to do with what the Advantage / Disadvantage system uses. Basically, you roll 2d20 instead of just the 1 and you take the better (or worse) of the two rolls. In 3rd Edition, some of the d20 games (Wheel of Time comes to mind) you had a Feat that allowed you to re-roll and (if memory serves) keep the best of the two rolls. The only difference there was that you didn't roll the dice at the same time, you just used the Feat / Ability to re-roll a potentially bad roll.
I started using it a few years ago to bring a much difficult challenge for my players and their higher level PCs. I love creatures like Goblins and I realize that most players don't think much about them after a certain level unless they are in sufficient numbers. I've employed strategic deployment in some cases where a higher, more intelligent power, was involved and a combination of a line of goblin archers and skirmishers can have a devastating effect on the player characters that don't exercise a bit of caution in combat. But in some cases, I want to do something more without necessarily adding hitpoints / hitdice or overly equipping them. In order to keep it simple, I figured out a while ago that rolling 2d20 and taking the better of the two rolls for purposes of attacks, certain skills, and certain saves will transform any creature into a much more devastating and challenging opponent. This opponent, because of the increased odds of success effectively becomes an 'elite' unit without necessarily changing any of his stats. At most, you can always max out the hitpoints for a creature of that type and that's it.
A squad of 6 'elite' goblins can be devastating to an experienced party -- especially if they get the drop on them. Careful though, a well executed ambush may even wipe out the party. ;)
So to sum up:
Elite Units get roll 2d20 for each attack and physical based save or skill check, keeping the best of the two rolls. Max out their hitpoints and you're good to go. As far as XP is concerned, I'd double that too. ;)
For a more detailed examination behind the math, I suggest Robert Conley's excellent post detailing the math behind Advantages/Disadvantages in D&D Next over HERE.