Steel discs

[Mindenbrush]

I get mine from Precision Wargames Supplies - http://www.freewebs.com/pwsltd/steelbases.htm

I used them for a special order on artillery train bases, just means you have to buy between 50 to 100 bases.

[DS615]

My brother and have been I using 1" steel disks for basing almost exclusively for a few years now.  I got around a thousand of them from an engine plant that closed down back in 2010.
They give lighter figures some heft and they're obviously receptive to magnets for markers or flight stands.  We really like them.