Angie, the Voyager program is one of my favorites. Daring, imaginative, and full of surprises. I love that they've both left the heliosphere and are now in the interstellar medium, but still sending some data home.
And here's another of my favorites:
Rosetta, the European Space Agency (ESA) spacecraft, traveled for ten years and billions of miles in order to rendezvous with a comet, accompany it as it moved through the inner Solar System past the Sun, and deploy a lander.
Rosetta the Comet Chaser