I've purchased RAM for my Blue & White G3 from Other World Computing, received a bad DIMM, returned and replaced without hassle. Today I just received my 500GB Hitachi Deskstar SATA for my PowerMac G5 Dual 2.7 GHz with 2.5 GB RAM from NewEgg.com. I am thoroughly pleased with the NewEgg purchase. You can compare NewEgg.com to MacMall.com or MacWarehouse.com, but NewEgg.com will be less expensive for many items. In my case, the same Hitachi hard drive on NewEgg.com was cheaper than MacMall.com by $30.00 (U.S.) and NewEgg.com had free shipping (2nd DAY!!!).
My recommendation is, find the hardware on a trusted Macintosh website, then search NewEgg.com for the same item, and be SURE the product numbers all match, else you may be sorry.