In an effort to keep the iPod frenzy going, Apple has gone so far as to offer lower cost devices like the iPod Shuffle. But Apple is not the only one standing to make some serious profits here. Nope, there are a variety of other companies riding on the backs of the computer company in an effort to turn a buck or two themselves.

Apple’s decision to release a Flash-based digital music player, the iPod Shuffle, was tacitly vindicated today by market watcher iSuppli. Its statistics suggest that solid-state players will continue to outsell hard drive-based units through to 2009.

Between now and then, overall MP3 player shipments will almost quadruple, from 36.8m units to 132m, the researcher notes in a new report, Portable MP3 Players: Booming Market Looks for New Twist.

In 2004, some 27m Flash players shipped, almost three times more than the 9.8m HDD-based units released into the marketplace. Come 2009, however, the proportions will have fallen closer to parity: 75.8m Flash players to 56.2m HDD-based units, iSuppli said.

The two categories will show compound annual growth rates of 22.9 per cent and 41.8 per cent, respectively. HDD shipments will show continuous, linear growth through over the next four years or so, while Flash’s growth will quickly slow.

That said, it’s clear from the price differential between Flash and HDD players that Apple was right to establish itself in the HDD space first. Flash may lead in unit shipments, but it’s hard drive player sales that are really driving revenue growth.