
The materials listed below come from the publication
EXPLORING FUNCTION THROUGH THE USE OF MANIPULATIVES, © 1994, Agnes Azzolino, ISBN: 0962359335.
It, as other material at mathnstuff.com is provided for notforprofit purposes at no cost to the user. Please remember to site the source.
A sample of manipulatives is shown below. Links to additional material are also listed. 
Click on the image to see an enlargement.  Start with a
coordinate plane printed on paper (1/2 page works well). Provide students with waxpaper and have them place it on the paper coordinate plane (positioned for the function at hand). Have them pointplot a function ON THE WAX PAPER. They have made their first function manipulative. Repeat the process with more wax paper and more functions, as desired. 
The function I use first is 1/x, x^{1}, the reciprocal function. The absolute value, and square root are also important, but, not as important as the big 3  the identity function, the opposite function, and the reciprocal. 
The Absolute Value Dilator at the left is made of printed transparency film with the 2 arms hinged by a clothing snap. Once placed on a coordinate plane printed on paper, functions such as 2x and x/2 may be graphed as well as the more traditional x, x+2, and x1+3. 
Click on the image to see an enlargement. 
The Slopemeter is also printed on transparency film and a tangent arm is hinged with a clothing snap at the origin. Placed on a point on a function and positioned so the xaxes and yaxes are parallel, the slope may be read by placing the arm tangent to the curve and determining where the tangent line crosses a grid mark on the coordinate plane. The (x,y) coordinates provide the y/x slope. 
Additional Resources

Good Stuff Page Math Languages, page 9 
www.mathnstuff.com/papers/langu/gwm/gintro.htm 