Avenger of Sin
Basically 4e is kinda like having a party of 3.5 wizards who dont know what spell to cast next and search through all ther spells to figure out what to do each turn...
Then they need practice, they need to learn to plan ahead, they need to play from level 1 so they can grow into their abilities.
I've now played in a Paragon Tier and a mid heroic tier (7-8 ending) game and neither of them had the players wait for more than 10 seconds before saying "I'm using X"
The best thing to do is either power cards, as Fox said, or do what my divine game did. Type up all the at-will, encounter, utility, and daily abilities onto a couple sheets (was two pages per character at 7th level with item abilities.) Then it only takes them a few seconds to review your available powers.
Also simple planning goes a long way. I was often able to offer the other players combat maneuver advice each round because I was paying attention to the board. And, since i was the Leader in both parties I kept track of everyone's damage as well as my own (they tracked their own as well) so that I wouldn't have to spend every turn starting off with "Who needs healed, anyone?" We knew what was happening so we could respond swiftly.
Alternately, if a player takes too long you can just rule that they use the first at-will on their sheet against the closest appropriate target. It will teach your players the value of swift decision making. If you do this though, make sure they know, and that they know how long a timer they have, don't just interrupt them one combat and go "too long, you magic missile the goblin to Todd's left." That would be annoying.
