White has Mirran Crusader at 3 mana who has Double strike, as well as Hero of Bladehold at 4 mana, which puts more creatures into play whenever it attacks! On its own, Blue doesn't have too much to include at higher mana costs. The Illusion Lord, Lord of the Unreal, only costs 2 mana, so you can easily assemble a mono-blue Aggro deck that tops out at 2 mana, allowing you to include more spells and less lands while still reliably getting the mana you need for any spell in your deck. If you're playing UW, you get access to Geist of Saint Traft for 3 mana, which is a 2/2 that summons a temporary 4/4 flying angel each time he attacks! Throw an Angelic Destiny on Geist and he can end the game in 2 turns!
With Angelic Destiny comes the topic of Utility. This is what makes the difference between a stack of creatures and land and a powerful Aggro deck. Sure, you can just throw all of your Goblins together and call it a day, but what happens when the game goes long? What if your opponent gets their blockers out early and you can't get that last few points of damage through? Enter Shrine of Burning Rage. This is nearly universally included in Red Aggro decks as a 4-of at this point. The Shrine gets a counter every turn and every time you cast a Red spell. If you can drop it on turn 2, it's going to slow down your attack, but it's almost always going to be worth it in the long run. After only a few turns and a few spells (almost all of which would be Red, mind you) you're going to be sitting on a 10 damage bomb waiting to go off in your opponent's face. By the time you need to eek that last few points of damage through, your Shrine will be ready for action! Some other Utility comes from Lord effects, like you see on Lord of the Unreal and Goblin Chieftain. When you're playing with lots of little creatures, this +1/+1 bonus can practically double your damage output. Other effects like Battle cry, as seen on Signal Pest can also have game-changing effects on the amount of damage you can deal. Finally, White has Honor of the Pure, which is basically just a Lord effect for all White creatures. That and a Knight Exemplar are all the Utility you'll need in a White Knights deck!
How about an example deck to close out the discussion here? I've neglected Black entirely in this article, so I'll show it some love here. Behold, Vampirism! Okay, it may not be exactly awe-inspiring, but it's a pretty typical example of an Aggro build. Check out the mana curve on the right. I'm stretching it a little bit here considering my mana base and going to 5 as my high end, though I've only included 2 of those. Everything else in the deck is 1-3 mana. I might do well to add a couple more lands in there to ensure I can cast my Anowon, the Ruin Sage when he comes up, but other than that, you should see a 1-drop every opening hand, either 2 more for turn 2, or a 2-drop, then curve into Vampire Nighthawk on turn 3. From there it's a cakewalk. Captivating Vampire is great against bigger creatures; why kill them when you can take them? There's some utility in the Blade of the Bloodchief, Captivating Vampire, and Feast of Blood, not to mention Gatekeeper of Malakir and Guul Draz Assassin who double as both removal and damage-dealers. And, of course, there are plenty of small, efficient creatures ready to take down an opponent's life total. That's Aggro for you.
So what's your favorite Aggro build? Do you play Red for Goblins, mono-Blue Illusions, or something more unique like Angry Kitties a la Loading Ready Run? Do you like mono-colored builds, or do you prefer multiple colors in your Aggro?