I always have a hard time building a good entrance to my fort. I want the bad guys to die and the good guys to move through unmolested. Inevitably I settle on a longish corridor with the trade depot at the back, but there must be a better way. Any ideas?
The best idea I've come up with is a two-way airlock. Put one bridge in the front, two in the back, with the trade depot in the middle. One of the rear bridges lets you access the depot or outside easily, the other is a long thin corridor lined with your favorite traps you can funnel enemies through (rather than let them sit outside and kill off your traders, migrants, and wood/ect access). You could also put a fourth bridge at the end of the trap corridor to make the goblins turn around and leave through your traps again, if you don't feel like that's cheating.

EDIT: Trap plan here:

Black is the part your enemies have to take, white is an adjacent pit, the gray square is some up-stairs to get out of the area, and red is up stairs or ramp from a lower level to get back to the trap path if the enemy falls off. Now you just have to stop your dwarves from running in there themselves.

You could also station dogs on little path two spaces long on the sides, to give the goblins more things to try to dodge away from.