How to Slice the Cheese

This is a special case of the problem of counting the number of regions $\mathbb{R}^n$ is divided into by $k$ hyperplanes in general position. The answer is $$\sum_{j=0}^n {k\choose j}.$$ This is mentioned in Richard Stanley's notes on hyperplane arrangements.

This was a very old Monthly problem - see below. For an excellent introduction to the general topic see Richard Stanley's paper An Introduction to Hyperplane Arrangements (2004) and also Renteln's lecture slides It All Depends on How You Slice It: An Introduction to Hyperplane Arrangements, 2008

This is the lazy caterer's sequence. As others have mentioned, arbitrary dimensional analogues are called hyperplane arrangements.