Alright, so I've found a world seed that spawns you in a forest, in which there are quite a few basins, a couple of which contain surface level iron! The seed was used in Marrilland's Hardcore 100 Diamond Challenge, and the entering of is shown here.
Yup, the seed is: "Toothpaste on my Teeth" without the quotation marks. This has been tested on 1.2.5 and 12w23b, so it should work on other snapshots too.
And now for diamond coordinates!
(Encased in Stone, not attached to a cave.)
(On the ground of a cave, next to a lava pool)
(This one has the coordinates of the blue wool of a desert pyramid that has diamonds in its chests)
More will be posted as they are found!
If you do try this seed out, and find diamonds not listed here, please post the coordinates.
(These coordinates are a safer place to enter, but are not right at the end portal)
(It is safe to dig straight down at the above coordinates until you reach the stone bricks)
Exact End Portal Coordinates
(There is a small cave in between ground level at the X and Z and the exact coordinates, but the cave is way above lava layer, so the only thing to worry about is the monsters.)
(These coordinates are exactly Z -1 from standing right on top of the Silverfish Spawner.
There are also many other cool things, including a few surface level lava lakes somewhat near the spawn!
I also discovered that within the boundaries of a map created at spawn, there is a stronghold between layers 40-50 inside a jungle. If you want the coordinates, I can get the coordinates of X and Z (It's safe to dig straight down until you reach the stronghold from the coordinates where I entered.)