I bought 10GB of additional memory (to fill all 8 slots for maximum performance) from MacRamDirect. The heat spreaders look very similar to the ones on the Micron RAM that shipped from Apple except they have 7 "fins" instead of 4.
Although MRD put on their own stickers, if you look carefully you can see through the sticker to the one they covered up where it says Transcend. The manufacturing ID from the SPD (displayed in System Profiler) also confirms it is Transcend. See this post for more info. I'm not sure why nobody has posted the manufacturing ID from memory being sold by OWC, TransIntl, etc. in that thread...