If you've never used or heard of a Hori Hori, now you have. It's the best all around hand tool for gardening. Of Japanese design, they were originally used for working around and with bonsai. You'll never use a regular old trowel again and because they have a serrated edge you can use it to slice through thick roots buried in the soil.
Make sure you find yourself spending about fifty bucks on one-there are some knockoffs out there that are a sorry copy. It should feel heavy and sturdy in your hand-the blade should be thick and made of carbon steel. If you're buying one online for twenty dollars don't expect it to last more than two seasons...Trust me, it's a good investment.