OEM is definitely worth it for hard drives. You'll save yourself a chunk of change, can download the utilities/drivers online, and you're going to use rounded IDE cables anyway, right? So you're not really missing out on anything, except the higher price.
Just make sure wherever you get the drives from provide the original manufacturer's warranty.
The utility package is usually something you won't use anyways. IDE cables usually come with the motherboard. You don't want to use round cables, because IDE cables are designed in a way that every third or fourth wire is there for stability(someone should really explain this, I know its true because I've tried it, but not the details). So if you use round IDE cables, you might get erratic errors, just stick to flat.