I like using Flash Pro as a level editor. My entity system detect movieclips which have particular syntax names, create an entity based on this syntax and pass the movieclip to it for the graphical reference.
I can give id to the entities to create links between them and I can pass some values too:

Flash is great to do random/procedural graphics, i've made some tests in the past:

http://accropix.free.fr/tig/rand1.jpg
http://accropix.free.fr/tig/rand2.jpg

http://accropix.free.fr/tig/creatures.swf

I use this principle for the enemies, trying to give them more personality:

[The concept:]

Hey! I would like to have some feedback on my first game (not yet named) about ideas and art.

The concept: You are a surgeon completing different operations with the most sophisticated medical tool ever: a miniaturized paddle and ball 

I want to do varied enemies, moving or stationary, with different behaviors, like launching things, adding blocks to the level, etc. For example, the green one has tears which heal enemies and blocks :

Missions will be composed of subchallenges, such as: time limit, destroy enemies only, destroy all blocks and enemies...

Levels can be played with the classic no gravity mode or with the gravity mode, where you have to use your paddle like a real racket (gif soon). The mode depends on the mission.