Well, I was just digging around randomly, then decided to dig down to bedrock for fun. In the middle of digging, i stumbled across a hole I thought might lead to a cave, well...as it turned out after clearing a few more blocks, it was a GIANT RAVINE :D Check it out and hope you guys share some of your cool dung/ravine/river/mountain finds here :)

http://screensnapr.com/v/1QgnpH.png <--- Ravine pic.
-EDIT-
Here's somemore :D

http://screensnapr.com/v/zzch3C.png <-- near end of ravine at bottom
http://screensnapr.com/v/4LmeRu.png <-- Going through tunnel in bottom corner of previous pic
http://screensnapr.com/v/aovVpq.png <--- a 2nd ravine branching from small tunnel
http://screensnapr.com/v/VEHfzw.png <-- My view of how the 2 ravines kinda branch/connect :)
-2ND EDIT-
http://screensnapr.com/v/Tecmj8.png <-- Lol ledge
http://screensnapr.com/v/xumNkV.png <---Interesting and kinda cool landform I stumbled upon.
http://screensnapr.com/v/menw23.png <-- Entrance to a mineshaft that I found in 2nd ravine
http://screensnapr.com/v/pAGD5q.png <-- another mineshaft off to side from first (Yes, there are some strange odd pixels in top corner, thats just the ScrnSnapr, not the actual game).
http://screensnapr.com/v/lPqHop.png <-- *giggle* creeper's stuck
http://screensnapr.com/v/NzVOSf.png <-- Chest I found in the mineshaft. Had 3 diamond, 2 cocoabeans, 4 redstone, and 12 iron ingots :D (or something close to that).
http://screensnapr.com/v/0xNEla.png <--- Eerie strange hole I found...
http://screensnapr.com/v/qaRMeM.png <--Left the eerie hole to explore, came back through later...Ooohh! Look who's there!
http://screensnapr.com/v/1lBEKE.png <--Ores Galores! :D
http://screensnapr.com/v/2ByJm8.png <-- Silly Zombie, Ledges aren't for kids.

-3RD EDIT-
http://screensnapr.com/v/g1yqOX.png <---Massive Spiderwebs
http://screensnapr.com/v/Ihoc4x.png <---Spider spawner
http://screensnapr.com/v/iuZeiQ.png <--- Dungeon...Then another across the way
http://screensnapr.com/v/8sljuh.png <--- Dungeon in middle of mines
http://screensnapr.com/v/kdozWg.png <-- My inv after finding all those dungeon/mineshaft chests. I only had 1 pick, 1 shovel, 2 swords, and the 5 pork/3steak. All the rest came from dungeons/mineshaft :3
-EDIT 4-
http://screensnapr.com/v/htTEUG.png <---Another Eerie Room\
http://screensnapr.com/v/tBGz85.png <-- Yea, ujellieh :D (100% legit find)
http://screensnapr.com/v/sBfYRn.png <-- Whoaaahh duuuuddeeee
http://screensnapr.com/v/zA0OGx.png <-- Lol devil mountain? :p
http://screensnapr.com/v/yno0QG.png <-- Could totally do a natural castle with that :D
http://screensnapr.com/v/mLdeLY.png <-- oohh mysterious :3
http://screensnapr.com/v/xqBmGW.png <-- SWEET.