Stanley's proof of the Upper Bound Conjecture relied on a connection with free resolutions of graded algebras. This has led to the very active area of Stanley--Reisner theory, where combinatorial properties of simplicial complexes are related to algebraic properties of certain graded algebras.
For references, there's a wikipedia page on Stanley--Reisner theory if you're interested:
http://en.wikipedia.org/wiki/Stanley%E2%80%93Reisner_ring
Also, Bruns and Herzog's book "Cohen--Macaulay Rings" has nice a chapter on Stanley--Reisner rings. I'm sure there are other good references as well.
