I Used to have no idea of any Monster when starting as a Dm, so: what i did was modify existing monters or make them up myself! this created a very fun Quest just going over 1 type of monster...
Swark:
Hp: 30 *
Ac: 19* (+2 dex,+5 Chainmail, +2 Heavy wooden Shield)
Attack: +6* (1d8+4 19-20 x2 Longsword) or Longbow +5* (1d8 , critical x3)
Special Qualities: Horde*, Scent
Saves*: F 8 R 4 W 4
Skills*: Spot +4, Listen +5, Craft (any, except alchemy) +7
Feats: Combat reflexes
Special Qualities: Scent, just like animals (Swarks got a nose jsut like a pig)
Swarks can be recognized by there distinctive noses, and when marching in large groups the marching is hearable 1 mile away.
Horde:Swarks gain additional Bonusses when fighting near eachother, for every Swark withing 100 ft, the Swark gains +1 to Hp, AC, Saves, Attack Rolls and skill checks. (So 5 swarks in a group means: Hp: 35, Ac 24, Atk: +11
Saves: F 13 R 9 W 9, skills Spot +9, Listen+5, Craft(Any,except alchemy)+12
The Quest: An Invasion of Hundreds (or Thousands) swarks begins, they take over city's in a rapid speed, peopple running for theyre lives, the guards to stand and fight, The PC's can fight them, but in the first encounter they will expierence the power of Swarks in groups...
They will: Retreat, Give Up, Flee, Fight.
WHen they retreat to another city, the swarks come up very rapidly and take it over, going on till" there are no more free city's..
Flee: Into the forests they are pretty much safe unless they attack.
Fight: They can fight but they will be captured and enslaved
Give up: They will ben Captured, stripped from gear and Enslaved
WHen the swarks finally captured them they must work in the mines to collect gems, they must work for food. The PC's Must escape the mine (Own Creation here) and they must/will flee into the woods.
When they flee into the woods they will find a Group of Wood Elves, the rebels, trying to free every city.
They must make up a Plan to get some sort of a Cohort or take over the city imediatly. (Place Own Creation here again)
They get support from the people, but the Swarks call in reinforcements:
Imperial Swarks (just slite stronger, got a full-plate and the Horde ability only works on other Imperials)
Swark Riders (riding on some sort of Beast, Horde ability only works on other Riders, else identicall to a normal Swark)
Swark Flyers: Fly on some sort of beast and throw javelins downwards to create a rain of javelins, Horde ability only works on other Flyers, else identicall to normal swarks)
Mages: Simply Sorcerers, Horde ability only works on other Mages (which are few) and got less Hp and Ac...
The Swarks (re)capture city's untill a breakthrough: Imperial Guards of the king come and help, the PC's get a huge help from them and (hopefully) force the Swarks back, (Imperial Guards are very strong, but against an army of swarks they are weak) Now the PC's come with a plan to free all city's and the whole country from those nasty swarks...(Own Input here)
Details: Swarks eat nasty food, but very nutricious, they also like beer.
After staying in a country for a long time, they become Lazy and won't work (that's why they enslave people...and let them work in the mines) they hate it when they they're being fooled (especially theyre noses are popular....) and will atttack.
Defeating the swarks is just: Breaking them up in smaller units in which they become very weak and can be killed with ease...(The Imperial Guards come in handy here...). The cohort can be: The wood elves (in the beginning), the wood elf leader (the whole time, uber-dude) on the way they may pick up some Fighters, Barbarians, Archers, Monks, Clerics, all sorts of troups and let them fight for them...
Also: If the Players do nothing in the woods the Swarks may come and seek for them, or the food runs out (swarks eat a lot!)
The Final thing: An "epic" Endclash with a staggering fight between the PC's and a Black Dragon....
This Quest is: Planning well, and then making the plan come true, it's exiting for the Players, because if they get snapped by a group of swarks they're toast....sometimes they need to hurry, other times they can laugh about the Swarks Noses...
Made it up all by myself and played it with my players....

it was great!
What do you guys think about it...??