One thing I've done to slightly speed up combat in 4E is to announce at the start of a fight what the lowest and highest Defense numbers the enemy has. Example: Orc Warrior has AC15, Fort17, Reflex13, Will12 and Orc Mage has AC11, Fort13, Reflex13, Will14. I would announce that the enemy has defenses between 11 and 17. This way the players know what rolls automatically miss or hit. If a number falls within the range I then ask what their target Defense was and then relay whether they hit or missed.
This method means when players roll a really high number, such as 25 against the enemies above, they don't have to wait for me to let them know they hit. Conversely rolling really low means they can move on, without having to check with me. However, there is still a sense of mystery when rolling as the players still do not know exact numbers and if they roll within the range, they can still hit or miss depending on which Defense they are trying to hit.