[nierman]

you could try PostGIS's spatial indices for a less manual/static approach.

spatial indices of the R-tree variety work quite well as long as the dimensionality isn't too high (i.e., your 2D data would be good).

note: the original 1984 paper on r-trees is a good one (although the performance section is a bit weak): http://postgis.refractions.net/support/rtree.pdf