The tools I use to manage depression are (wait for it) diet, exercise and prayer (or meditation, if you want to keep it secular).
Exercise is particularly useful. Depression affects the mind, so it's difficult to be self-aware about it. But I've found that when I start to have those thoughts of hopelessness, going out and running 1-3 miles at a pace that pushes my physical limits (I use a Nike Sportwatch for measurements) eradicates my depression.
On a semi-daily basis, 30 minutes of prayer, 30 minutes exercise and at least one meal with ~90g of raw spinach seems to do the trick for me.