A very nice map that sits in your HUD. You can also set way points.
Customization mod to improve frame rate and other video settings.
Minecraft Forge A Minecraft launcher which can load mods dynamically without changing or patching the minecraft.jar.
LabyMod has a wide range of features that will make you want to use it, from toggle sneak to 1.7 animations it has a bit of everything. You can view their features on the website.
Toggle sneak allows you to stay in sneak mode without having to hold a button down continuously. Improved chat brings a longer scroll back, special characters, the ability to turn chat off/on, copy/paste plus click on links.
5zig is a ui for displaying useful information to you without having to enter debug mode, you can enable being able to see your current x,y,z, your direction and much more useful information!