Encounter tables are a fantastic way to define an RPG setting; they're experiential instead of narrative, and serve useful campaign defining purposes both in their creation and use. They're extremely economical in terms of presenting useful setting information in a compact space. But they're not without problems. The traditional wandering monster table requires the DM to improvise an entire encounter right on the spot and there's not much with which to work. As Brendan pointed out in a previous comment, a result of 8 orcs, range 70', reaction roll: 9, is fairly bland as a starting point.
What can we do to make those encounters more interesting?
My first thought was to have a simple "monster motivational chart". Imagine you're a simple Ogre named Pigswallow, just trying to make your way in the world. What motivates Pigswallow to abandon the comforts of lair and den, joining the ranks of wandering monsters everywhere in search of better things, and risking a dangerous encounter with adventurers?
Monster Motivations (roll 2d6)
2 Seeking spiritual or intellectual fulfillment
3 Searching for mates
4 On guard patrol
5 Seeking a shelter
6 Looking for water
7 Looking for food
8 Looking for warmth, comfort
9 Looking for treasure
10 Looking for lost companions
11 Out to prove their worth
12 On a quest for knowledge
It's pretty basic, but you can see that rolling a motivation for Pigswallow (and interpreting through monster psychology) could help with the encounter embellishment. I rolled a friendly reaction (12) and motivation food (7), and suddenly Pigswallow is magnanimous, since clearly the player characters have brought their rations as offerings to avoid his lordly wrath; a similar roll of 9,9 leads to a somewhat friendly Pigswallow, as long as the characters are willing to pay him to go away, and so forth. I'm not sure what "spiritual fulfillment" looks like for an Ogre, but it would be fun to improvise. The table is only there to help with intelligent encounters, although maybe something similar could be built for animal behaviors.
The second problem involves what is the party doing. There's this false assumption that just because the player's announced a marching order, they spend their entire time in the dungeon in perfect formation, with perfect spacing, never deviating from rank and file, ever ready for anything. No one ever relieves him or herself, there's no breaks for water, no one drops a piece of equipment, and the lights never go out. You have carte blanche to roll on a table like the one below any time there's an encounter to see what's really going on with the party at the moment the encounter is detected. (I posted a larger version of this table, for wilderness encounters, here: Too Busy Looking at the Map to Notice the Monster).
What is the Party Doing? (roll 2d6)
2 Changing over a light source
3 Drinking water
6 Scouting ahead
7 Exploring and alert
8 Talking and walking
9 Walking too close together
10 Someone just tripped and made a loud noise
11 Equipment problem
12 Taking a break
Of course, I think the ideal situation to the wandering monsters is to come up with a few pre-planned encounters for each entry, in advance. For the Black City, where many of the encounters in the early game were competing explorers, I have 10-12 encounters pre-made to cover bandits, veterans, traders, NPC parties, etc. It was a fair amount of time invested, but really paid off in play. Another approach for monsters, particularly ones that wouldn't have motivations represented by the monster table above, would be to come up with a few specific dispositions so each encounter is a little different.
For instance, gjengangers (Norse zombies) are pretty common in the Black City; here's a sample table I could see myself using to determine what the gjengangers are doing whenever their number comes up on the wandering monster table:
Gjenganger activity (roll d6)
1 Shambling toward the player characters. Brains!
2 Lying still like dead bodies on the floor
3 Crawlers, pulling themselves forward by their arms
4 Milling around senselessly until aroused
5 Busy messily eating something else
6 Lurking in a niche or around the nearest corner to lunge out
I'm sure someone out there has done a bang-up job of creating ultimate wandering monster encounter tables, but it's so easy to lose track of the tribal knowledge out there in the wilds - between the blogs, message boards, zines, and other publications. I'd love to hear about some of your favorite expressions of good encounter tables that you've seen in use. I'll think about it as well and reply in the comments.