<< among companies that make 512, which one is best, most reliable, etc? >>
Since Crucial is out of the picture on 512 DDR, try Mushkin or, if you can find it, Infineon. 512MB sticks have really jumped in price in the last 2 weeks. Even high quality Infineon sticks were $55-$60 a short time ago, now expect to pay $110-$120 for decent stuff.