What do you mean by clones? If they have the same content, are they mirrors? If they have different content, how do you expect or want it to be different? Is the existence of Conservapedia a good thing?
Most large public wkis are "Wikipedia clones" to the extent that many of them use the same software/wikitext standard (MediaWiki), article naming conventions (which allows guessing the name and linking to an alternately-hosted article by simply switching the InterWiki prefix) and/or licensing (allowing for both mirroring and for sharing derivative versions)
The easiest way of supporting such clones today is probably donating to promising efforts (many of these now exist, albeit with varying levels of compatibility) and supporting CreativeCommons, who manage the underlying legal infrastructure making comprehensive "clones" possible in the first place.
I donated to Wikipedia before. However, this year, I'm not donating, and my rationalization is this: there need to be more Wikipedia clones on the internet, to best prevent the possibility that a single organization (Wikimedia) abuses its control of the biggest worldwide information source. Thus, instead of donating to Wikipedia, I would like to subsidize potential Wikipedia clones. Whether or not it has ads is of little concern to me.