Not free but inexpensive math (visual spatial especially) manipulatives. LovedtoDeath on the WTM forum pointed these out to me. McRuffy Math Manipulatives
These include tanagrams for $1.25, pattern blocks for $2.00, etc. There are many patterns for geoboards, pattern blocks, tanagrams and similar free online. These can also be used to explore geometric and visual spatial concepts all on their own. The site also has pretty inexpensive materials for many of the manipulatives as well. You an also find patterns online to print your own manipulatives on cardstock. If you laminate this might work well for some manipulatives.