Minecraft Auto Run Mod
The best Minecraft mods in my opinion are the mods that don't necessarily change the way Minecraft works in wild and crazy ways, but the ones that add subtle functionality that fixes existing problems. Doomspork's Auto Run mod is one of these mods. It's quiet, unassuming and may have never made it to prom, but it's worth having by your side when push comes to lava pool shove.
This is not to commit the blasphemy of criticizing Minecraft. Most of Minecraft game play is a joy, like petting a new born lamb. However there is one aspect of Minecraft that can become tedious, and that's holding down the W key so that you keep moving forward over the endlessly generated terrain. Say you've built buildings incredibly far away from one another, getting between them can be a regular pain in the rear end. (I notice that a lot of male Minecraft players tend to build super structures at incredible distances from one another, so unless you have the Minecart Driving Mod you'll be stuck there for minutes on end, running along a silly long raised bridge.)
The Minecraft Auto Run mod adds the same sort of basic auto run functionality that you'll find in World of Warcraft, where the num lock key also doubles as a carpal tunnel prevention device.
Doomspork's Auto Run mod is set to the Z key by default, but it can be remapped in the options interface if you'd prefer it was somewhere else on your keyboard. With Auto Run engaged, you'll keep moving in a single direction whilst retaining full access to your inventory, being able to use items, attack and jump.
As someone who has often wished that there was some way to free my hands whilst roaming through Minecraft, this mod is a welcome relief. You'll still have to deal with the fact that bumps are generated every few feet and you'll probably fall into a lake and get deceased if you wander away from the computer when you have this mod enabled, but with great auto run power also comes great responsibility. If you abandon your post the best case scenario is that you spend hours running into a small lump of dirt, worst case scenario you take a flying leap into lava and lose all your diamond tools.
Think of it like real life. Actually don't, real life very rarely has auto run, unless you're in a car or bus or plane and someone else is driving, which isn't really 'auto' so much as 'completely powerless as to your own fault until you get out of the vehicle and regain autonomous locomotion.' Damn life, you scary!