The best way to deal with creepers I've found is to whack them and then back off while they're hissing, and then dart back in and whack them again. They expand sideways whilst building up to explode, so if you see it doing that, back the heck off.
Still hasn't saved me from getting blasted off ledges or ambushed by the bloody things as I walk out of my door.
Skeleton archers...them I do hate, I can't get close enough to whack them before they've dealt me heavy damage. The only thing to do is play them at their own game and fire arrows back at them.
Oh, and if you come across something looking like this:
Watch out! It's a mob spawner and it will spawn infinite amounts of monsters (although usually at no more than three or four per time) until you are able to destroy it. The loot in the crates can sometimes be worth it though.
