This is, by far, the most amazing seed that I have ever seen generated in Minecraft -- and it was a complete accident that I stumbled upon it. It's called AetherTestFirstWorld (I'm sure you can guess what it was for) -- and it's full of a little bit of everything.
My starting coordinates were (they seem to change, but not too drastically):
Here is the first set of screenshots...
If that interests you, here are more:
The screenshots don't do it the justice it deserves. You have to see this seed firsthand to really get the full feel of it. Give it a try -- you won't be disappointed.
The best part of it? The entire world seems to be just like this area.
Truthfully I was hesitant about titling it like this, but it's no exaggeration, I think. I've been disappointed by so many seeds posted on this forum, and after coming across this one I knew I had to make a thread about it. There's much more to it than even ten screenshots could show.