Soldering Iron Maintenance
A much cheaper option than the metal shavings coated in flux, is to put a pan scourer like this one:


(source: hospitalitywholesale.com.au)  

in a small container, and use that to clean the excess solder off of the tip, it seems to do a reasonable job and doesn't cool the tip excessively. Although you don't get the benefit of the flux which coats the shavings either.

(A tip: make sure that the scourer isn't plastic!) ;-P