IN THE GARDEN
If you, unlike me, have anything more than a balcony for little plants, you can use your grounds as a fertilizer in your garden and on your lawn; the grounds provide extra nitrogen for your sprouting greens to absorb. They apparently have great ability to cultivate mushrooms as well, if you enjoy growing them. Sprinkle it lightly on the soil or lawn before watering or rainfall to achieve the best results.
For those of you who compost, adding coffee grounds to your compost pile is an effective way of speeding up decomposition as the acidity increases and nitrogen. If you've got those lovely worms in your compost bin, make sure to give them the grounds as well (apparently pre-rotted is preferred) - they love them! Rumor has it that most flowering plants enjoy soil composted with coffee, and bloom brighter and stay healthier longer. Give it a try!
While you're taking care of your garden, you can curb snail or slug problems by circling your plants with the grounds. Apparently snails and slugs don't like the grounds and will back off. Ants seem to be repelled by it too - if you have an ant hill or hole in your yard, sprinkle the grounds on and around it. Apparently this is ant-speak for "go elsewhere, please!".
Coffee grounds can be used to remove odors from hands or in the fridge. Rub the grounds on your hands before washing to get rid of strong smells like onion, and put a small tub of grounds in the fridge to help absorb pungent food odors.
Using coffee grounds as an after-shampoo rinse is said to give darker hair extra shine.
And the best use that I've found so far (tried and true, tested by yours truly!) is using coffee grounds as an exfoliant - especially in areas where cellulite is present (ahem, not that I have any... doh!). You can use it as a facial scrub (mix with your favorite cleanser) to help slough off old skin and make your face softer and firmer. Caffeine is a vasoconstrictor and it will temporarily tighten skin and reduce dark circles (try it around your eyes!).
For areas with cellulite, mix coffee grounds with liquid soap and use your hand to massage it on the skin. You'll come out with firmer skin and a bit of a caffeine buzz - it DOES help a little! (Expensive cellulite creams are chocked full caffeine, which temporarily dehydrates fluid from fat cells, making them look smaller.)
Caffeine may protect against sun damage to skin cells. Try rebrewing your old grounds and adding it into your sunscreen or lotion. Couldn't hurt!
Special note: word has it that you can get coffee grounds from any Starbucks location if you just go in and ask!
If you have any tips or tricks for using coffee grounds, please share them!