Well, there's always more swap, but that's an option of limited utility. Perl data structures are reasonably large (I'll put in the obligatory plug for Devel::Size here) and it's pretty easy to chew up a lot of memory quickly.

An iterative algorithm is probably more in order if you're blowing memory or, if this is a program that works on the same set of data over multiple runs, you might want to consider something more persistent and less memory hungry, such as a database, that you can connect to and only process the data you need to.

(Or, if this is math heavy, consider something like PDL which can represent a lot of numeric data densely)