I vote for http://cedet.sourceforge.net/srecode.shtml
It has very clean syntax and has access to code environment through Semantic.
Also it is a part of a large well supported CEDET distribution (which was built into Emacs for 24.x version series).
UPDATE YASnippet is also a powerful template engine. But it uses an ugly file naming schema (your file name === template name) for you can't put several templates into a single file and have issues with national character sets...
