Snowball

Snowball is a vanilla item.

Obtaining
Snowballs can be obtained from fishing in the Jerry Pond, as well as from Snow Minions. You could also obtain them by using a Taiga Biome Stick, then using a Weather Stick to change the weather to rain, which would result in snow in the Taiga, which can then be harvested.

Another way to obtain snow is by buying Snow Shovel from located at the Mountain and using it to create snow layers in your island to collect.

Info
In Jerry's Pond, if you pick up snowballs and you have Frosty the Snow Cannon then instead of picking them up, it gets filled by 1 for every snowball.

Snow Block
While not possible in a crafting table, with a Super Compactor 3000, a Snow Minion will craft 10 stacks of Snowballs into an Enchanted Snow Block.

Trivia

 * It became commonly accessible with the 0.7.5 update. However, somewhat unknown, it was actually obtainable before then by using a Taiga Biome Stick, then using a Weather Stick to change the weather to rain, which would result in the snow in the Taiga, and then harvest the snow.