Using Snow Golems allow you to have an infinite amount of snow. Here's how to use it.
1. First, you need to find a suitable biome. Remember that deserts, and the nether kill Snow Golems, and in Plains, Swamps, Beaches or Mushroom Biomes, they will not leave snow trails. If you want to you can try seed 404. If you're stuck in bad biomes, you might be able to build a platform over a river -- Rivers count as their own biome (check the debug screen).
2. Make a 1x1x2 hole. This will be where your Snow Golem is. Dig a stairway or path such that you can see (and dig at) the future golem's feet, but it can't leave. If you're working on a platform, try making a 2-high cage of fencing, with stacked fence gates for access. Either way, you should have cobblestone as a floor, or some other block that doesn't dig quickly with a shovel. Snow won't form on upside-down half slabs.
Alternatively, place a block, and place blocks which surround the golem's head. Make sure you leave a gap in between the bottom block and the head blocks, so you can remove the snow.
3. Craft 2 snow blocks, by placing 4 snowballs on each space of your inventory screen. Stack them in the hole or cage. Make sure the hole is secure (no exit for the golem), and add another block, one space above the top of the hole (that is, 3 blocks above the hole's floor). This will not only prevent the golem from jumping (while letting you peer down at it), but protects it from rain, which would melt it.
4. Finally, put a pumpkin (Jack-O-Lanterns also work) on top of the snow blocks. The golem will form and shrink down to two blocks high.
5. The snow golem should spawn snow under its feet (as of 1.5 this doesn't happen in desert, extreme hills, or extreme hill edge biomes). Observe that if you dig the snow under his feet, the snow respawns instantly. You can hold down dig to continuously generate snowballs.
6. Keep doing this, and you will have unlimited snowballs (at least, as long as your shovel holds out). Snowballs can be used as a projectile or to make snow blocks. (There is a slight bug where if you dig at just the right angle, you'll dig at an accelerated rate causing your shovel to be used up very quickly while creating massive amounts of snowballs.)
|NiceMarkMC's Automatic AFK Snow Farm Tutorial (for mass production of snow over long periods of time) Video (view on YouTube)|
|HybridCraft's Tutorial Video (view on YouTube)|
|DJ&Riggaz Method Video (view on YouTube)|
|Another Snow Farm Tutorial Video (view on YouTube)|
|MikiMiner's Tutorial Video (view on YouTube)|
|DanielKotes' Fully automatic AFK snow farm tutorial Video (view on YouTube)|
|Docm77's snow factory tutorial Video (view on YouTube)|