Driveways and Sidewalks
Make a clean sweep of it
You work hard at making your house look attractive. So why settle for the "permanent" grease or oil spot on your concrete driveway? Get rid of it by pouring mineral spirits or paint thinner on the dirty area. Make sure it covers thoroughly. Then take a bag of of cat litter, sand or large box of baking soda (even corn meal will work - you just want something dry and absorbent) and spread it on the top of the spot. Leave it there for 12 hours or so and then sweep it up. The oil spot should be "gone with the litter". Get up the final traces of the mineral spirits with warm water, regular detergent, and a mop. You can us this method with dry cement, too, but in that case, let is sit for a couple of days before sweeping it up.
Better safe then scar-y
If your not sure what surface material your're dealing with, it's best to play it safe. Many commercial products are available for cleaning concrete, blacktop, and various types of patio surfaces. These can be bought at hardware and some paint stores, and should tell you right on the bottle if they can clean your surface without scarring it.
Foil that dripping oil
Oil is a tough enemy to face in the trenches of stain warfare, particularly when it has soaked in a good and deep. But here's a secret weapon that just might carry the day. Fix up a solution of one part TSP (trisodium phosphate) to four parts of water. Soak an old towel in the solution, lay it over the sinister stain, and allow it to sit. From time to time, you can work the solution into the stain with a scrub brush, but the best results will come from the towel leaching the stain out. Even if this does not completely remove a deep stain, it will reduce it.
A spot of trouble
For a stubborn grease spot, try scrubbing it with concentrated detergent suds. Use a very stiff brush, and then hose it down with water. Or you might try automatic dish washing detergent. Spread the powder onto a dampened surface and allow it to stand for a while. Take a bucket of boiling water and rinse the area, then scrub it and rinse it again.