Well, since you guys are all clamoring for Vanilla additions, I figured I should share a few mods I discovered while searching for updated mods for 1.6.2. These are the type of mods that you don't think you'll need, but you'll probably notice it if they're gone. Most of these I think should be in the vanilla game.
Multi Mine: This changes the way you mine blocks. If stop mining partway through, the block will remember how mined it was, so you can continue mining it without having to start over. If you make a mistake, no problem, the block will gradually heal itself if you leave it alone. Invaluable while obsidian mining, especially if you're being pushed away by water currents.
http://www.atomicstryker.net/multimine.html
Matmos: Matmos constantly scans the blocks around you, and plays atmospheric sounds appropriate to where you are. For example, it plays rushing waves and seagulls when you're close to sand and water, howling wind when you're in mountainous regions, and drippy, danky sounds when you're deep in caves.
http://www.minecraftforum.net/topic/379925-162-matmos-r25-environmental-sound-atmosphere-simulator/
Smart Moving: Gives your characters mountain climbing skills and more animations, and two extra buttons (Grab and Sprint). Using the grab, you can vault up 1-block heights without using jump, amble over 2-block high walls, climb up 3-block high walls by jumping and grabbing the edge, or scale 4-block high fences by crouching, holding jump, releasing jump, and holding the grab button once you're up in the air. You can also crawl through 1x1 block holes, double-tap 'A', 'S', or 'D' do a quick-step in that direction, or get an extra burst of speed by holding the mod-specific sprint button, even while using vanilla sprint. The mod also reworks swimming and flying physics with added animations, and a few other neat tricks (Diving head-first, hanging off of iron grates and closed trap-doors, sliding along the ground)
http://www.minecraftforum.net/topic/361430-164smp-smart-moving/
http://www.minecraftforum.net/topic/738498-164api-player-api/
You'll need Forge for all of these, the 'Installer' jar file will add a Forge Version of Minecraft in your Versions drop-down box in your Minecraft launcher.
http://files.minecraftforge.net/
Honourable mention goes to RedPower 2, this is the only major content mod I've felt kept to the spirit and theme of Minecraft, and yet added many new features (Integrated Redstone circuits, micro-blocks, Mobile frames that can move other blocks, Buildable computers) to help you build complex machines with simple parts. Unfortunately, the mod author, Eloraam, seems to have fallen off the face of the earth, the last update was for Minecraft 1.4.6. However, many mod authors have written copy-cat mods, including Project Red.
http://www.youtube.com/user/Eloraam/videos
http://www.eloraam.com/
http://projectred.endermedia.org/