My favorite stain fighter is Spray'n'Wash, which I buy packaged with the big refill bottle at Costco.
I also love Carbona Stain Devils, especially the formula for ball-point ink: works like a charm!
The absolute best for getting out greasy stains is Dawn dish soap. It's one of my all-time faves. Just treat the stain and let it stand for 30 minutes, or even better, over night.
And if you're feeling especially fastidious or fussy, Martha Stewart has some great suggestions for getting stains out on her "Stain Removal Basics" chart.