My group liked 4th Edition's tactical gaming aspect so much that they instituted a house-rule: even if your turn still hasn't ended and you still haven't rolled any dice, once you declare your action, you can't change it.
Here's an example:
"I'm gonna attack that Hobgoblin with Eldritch Blast. No, on second thought, I'm gonna use Dire Radiance!"
"You can't, you've declared an Eldritch Blast."
Of course, since I suck at planning ahead, I'm the one who suffers the most with this rule.
Meanwhile, the DM, who doesn't have to declare anything, happily changes the actions of the monsters - like when a skeleton shot an arrow at the group's Swordmage, and then the DM realized that the Fighter was giving him cover, so all the other skeletons immediately shot the Fighter instead of their original target.