If there is gunk on the lens, I generally just lick it off. Okay, in reality, I use Kodak Lens Cleaner (CAT 176 7136) if there is serious dirt on the lens after using a blower brush. If it is very stubborn, I'll put a drop right on the dirt and let it soak through, but normally I put the cleaner on a polish cloth or lens paper patch...
I only use the above method if the lens been splashed in some way where there is serious sticky gunk.
For normal cleaning I use a Lens Pen. I find them to be very useful. One end is a brush, the other is a microfiber cleaning pad with an embedded dry cleaning solution that replenishes itself when you replace the cap.
Several manufacturers make them. Here are a few.
Nikon:
http://www.amazon.com …in-20/002-8006849-5242438
Lens Pen:
http://www.lenspen.com
Leupold:
http://www.thesportsauthority.com …ndex.jsp?productId=852308
The microfiber is safe. The way a lens gets scratched while cleaning is when you actually rub the tiny dirt particles around on the lens. A polish cloth, lens paper, or microfiber surface cleaner will not scratch the lens unless there are small particles on it so if there is some serious dirt on the lens, use lens paper patches and change very often. Once the "chunks" are safely removed, use a dry patch to remove the residue from the lens cleaning solution and then once it is dry, switch to the lens pen to remove any remaining streaking.
Or, use my patented licking method.