I watch for cheap prices on Lens Pens, as I keep them on hand for cleaning eye glasses and cameras on the run. Anything in the sub $5 range catches my eye.
The lens pen sports a retractable brush at one end and a cap-covered, lint-free soft wiping element at the other. It is compact and protected enough to live in a pocket or glove box without collecting ruinous amounts of dust. Number of useful cleanings per pen varies on the size of and what I'm cleaning, but I tend to get quite a lot of careful use out of them. Grease and oil that gets picked up by the wiper don't get cleaned off, so over time you'll need to replace the pen.
I clean big lenses at home with a blower, lens paper and cleaning solution if needed. It'd be a waste to use one of these. In the field, however, this little guy shines.
