This is way better than anything I've ever read. Thanks Trevor and Macintouch.
Trevor Inkpen CanadaRAM.com
Apple does not manufacture RAM, they purchase RAM wholesale from companies like Samsung, Hynix, Micron, IBM and Elixir. They do not and have never used Crucial RAM. (Crucial bases their advertising on the fact that Crucial is owned by Micron, who does sell Apple some RAM). You really can't say that a particular brand, 'Kingston' for example, does or does not work in Macs. Each company has hundreds of models, only one or two are correct for a given Mac. Kingston only guarantees their KTA- series memory for use in Macs. Their PC-generic KVR- series are specifically not guaranteed for Macs. Most bad reports result from using the wrong model RAM in a Mac.
One poster alluded to third-party RAM meeting or exceeding Apple's specs. There's a problem with this. A given RAM module that works in the PowerMac G5 may fail in the iMac G5 - despite having the same paper specification, in practice the two Macs have different tolerances. 'DDR PC3200 CL3 JEDEC compliant' does not adequately describe the criteria for compatibility. The RAM's internal organization and the programmable logic make the difference. It's like saying that a wheel for a Ford has to be 'steel, 14' diameter and 12' wide', without specifying the bolt pattern.
There is no way to look at specs and determine accurately if the RAM will be Mac compatible, the only way to be sure is to test it. Buy RAM only from a seller who guarantees that the RAM has been tested and is compatible with your model Mac.
Choosing PC Generic RAM (including Kingston KVR-, Crucial non-Apple models and any number of other brands) has a problem - the brand of chips used, and the design of the memory board sold under that part number, is liable to change without notice. And these changes can make them fail on Macs, especially 'sensitive' models like the Mini, iMac G5 and 1st gen. Aluminum PowerBooks. So, if your buddy buys RamCo ABC2345 memory and it works, you could buy the same RamCo ABC2345 part next month and it wouldn't work because it was a different design.
So it is impossible to predict whether a RAM part will work in a Mac UNLESS the seller provides a written guarantee that it is compatible in your Mac. (Auction sellers, PC shops and big-box and online discounters are less likely to provide reliable compatibility information). It's also impossible to make a blanket statement that 'Brand Y' is good, or bad - because it is down to choosing the correct model.
Finally, keep your Apple RAM so you can reinstall it when you send the Mac in for warranty repair.