There's any number of reasons why combats can go poorly in 4e and most of them you don't want to mess with, because either the players did something good or the rolls went poorly.

I'd advise ignoring XP always, except (in 4e's case) for balancing encounters beforehand. You can always add in more monsters later.

I don't like Surrealistic's advice to use ranged minions to cancel AoEs. Controllers are made for blasting minions and by using lots of ranged minions, you're just punishing that character for doing what he's supposed to be doing. Just use more. Give yourself a maximum amount of minions to throw into an encounter. Throw in more as combat progresses/as needed, but if the players are steamrolling due to good rolls or good teamwork, lay off and let them steamroll. This ties in with the XP advice; you don't have to worry about minions too much, just use them to ramp up the difficulty without negating good planning, good roleplay, or making combats longer when victory is assured.

Use terrain. Not difficult terrain. All sorts of terrain. "If you stand here, you are weak to fire but you do +X cold damage". Traps. Things that PCs can use but can bite them in the ass, with NPCs with slides and pushes and pulls to make those things more dangerous.

As, as Farland said but didn't really explain, the MM1+2 and DMG1 monster damages are all too low. Surrealistic probably had the right numbers.

I'm also a fan of Soldier-type NPCs. Use them to frustrate certain players and make the team adjust.