Love seeing all of the responses here.
I start tons of seeds indoors, so one of my favorite tools are seed spoons. They are so helpful for managing those tiny seeds and getting them placed exactly where you want them. I have a set of 2 (from Lee Valley) that allow for 4 different sized seeds.
I also love my Haws professional watering can (I have the english, metal version). I love the long arm that allows me to water my seedlings so gently, and makes it easy to reach to the back of the flats. In addition, they have a great balance, so it makes it easy to manage the can even when full.
