I've used a plethora of different creatures just by changing the names of things in the Monster Manual and slightly adjusting the effects of certain things. (Damage types, for example).
In a current adventure I'm running, the PCs (lvl 8) are to be confronted by some elves. Instead of trying to bump up the elves 6 levels, or making some from scratch, I just used the Eladrins in the MM and called them Elves. Swap out Fey Step for Elven Accuracy, give the Fey Knights a Longbow ranged attack, remove the Incanter's Spear attack, and be done with it.
I needed a giant octopus for an underwater encounter, and a Grell worked just fine. Just removed the Poison keywords, and Blindsight. Change the Fly speed to Swim speed, and added a simple Encounter Power(Close Burst 1) that provides total concelament until the end of the Octopuss' next turn, and called it Ink Cloud.
Basically, I've found there are enough monsters of assorted types in the MM that it's much easier to tweak some things than to try to create from scratch. Just use the same role(skirmisher, brute etc) from around the same level and the only changes you need to make are for flavor purposes.
Later
Gruns