I've long since moved far, far away from efficient construction.
My living spaces have lately incorporated a three-z-level format. 2x3 townhouses are laid out in visible avenues, with up and stairs interspersed between them. These lead to either similarly designed structures or legendary/champion manors. If a water source is available, I may dig the level below out to resemble a canal and place peasant housing alongside it.
Workshops are given individual walls and doorways (good for isolating failed strange moods!), and are typically branched off in an opposite direction from the residential area. Fancy meeting areas are placed wherever possible; yes, the parties are annoying, but it keeps moods up and looks quite spiffy.
Joining the two distinct areas, I like to place a massive meeting hall with all the trimmings; platinum statues, artifact items (which aren't already in noble rooms), and such things. The Trade Depot is usually adjacent, and is every bit as lavish (you gotta make a good impression on them merchants, y'know?).
One goal I keep in mind with each fort is to leave a direct path from the entrance to a spot reserved for the ruling noble's throne room and personal space. I haven't been able to get a ruler to appear in this version ( :[ ), but when I do, I'll be ready. : D
The primary mineshaft is typically plopped down in the middle of the aforementioned central hall. The prison and barracks are often set down a few z-levels, but not far from the shaft itself. The tombs are even further than that, and are smoothed and decorated for even the most lowly dwarf. (The proletariat often have clustered burial chambers; soldiers, legendary craftsdwarves, and nobles receive individual monuments with varying levels of bling.)
That's all urban design, though. When it comes to small scale architecture , I'm personally a fan of multi-z-level complexes, diagonal room corners (which can be just gorgeous with a good tileset), and the odd extended corner or staggered wall. Lately I've been playing with above-ground forts, and I'm considering trying to design a star-fort style layout. Marksdwarves and fortifications can stand in for the cannon ports, but by using multiple entrances and overlapping fields of fire, it wouldn't be hard to both split up siege squads and funnel them into kill zones.
It's easy enough to get a fortress to have substance, but style is another game entirely. : )