Online resource for Algebra activities

I want to share a web resource called Yummy Math. Although it is geared towards a K-12 audience, the Math activities seem very interesting and High School level activities seem appropriate for our students as well. I especially like the Algebra section and the cellphone plan comparison activity

Excerpt: 

"This lesson makes a great intro to linear relationships.  Student pick one plan and consider the cost of the phone and plan over time.  They make tables, graphs and equations.  Consider allowing students to begin playing with the task without much initial direct instruction.  Guide them with good questioning and teach after they have had time to grapple with these questions and construct new ideas.

After students select a plan and complete their graphs consider posting the graphs up on the wall (or over a document camera).  Have the rest of the class identify which cell phone deal matches their graph.  Finally students compare paying for the phone up front with T-Mobile versus going with a contract.  Which is cheaper over the long run?" [Activity details]

Have you used similar activities to broach algebraic concepts with your students... Please feel free to share your favorite resources below. 

~ Priyanka Sharma 
SME, Postsecondary Completion