The TI-84 graphing calculator. In snoburbia, every student in Algebra 1 or above is required to have one - at $99.99 apiece.
The TI-84 is a gold mine - but not for math. The real benefit is that snoburban dads can use it to drop how advanced their kids are in math. Bonus! For example, this recent listserv request: "Does anyone have a TI-84 calculator for my 7th grade daughter who's in Algebra I?" Or this article disguised as a rant against the costly TI-83:
I turned to my Daughter. She's just finished 9th grade pre-International Baccalaureate Geometry, and also has a mandatory TI-83 graphing calculator.
Some enterprising youths have made a killing on eBay with my son's TI-83 calculators - four stolen in two years. My husband is convinced he has bought back the exact same calculator four times.