When I bought my eMac I made the mistake of not going with a bigger hard drive and settled for a measly 40GB. I thought then that this would be enough, but the more pictures I stored on my computer the quicker I was running out of space.
After a couple years of fruitlessly trying to save space on my computer, I bit the bullet and went out and bought an external hard drive to the tune of 250GB. It's a Western Digital MyBook and it's working great with my eMac. And it only cost $139 at Staples, but well worth the investment. No software to install either...just like plug 'n play. And most important...it's fast.
The only problem encountered is that it doesn't much care for OS9 Quark 4.0 files. It can store them, and retrieve them, but saving changes to the file after retriving it from the external hard drive can be a little tricky. So I just save a copy to my desktop or internal hard drive and work on it from there, and then save it to the external hard drive for storage.
Other than this I'm pretty satisfied with my choice. It's gonna make my workflow that much more easier and effecient. I just wish I hadn't waited so long to get one.