Apple shops around but their Desktop drives seem to mostly be Seagates for the past few years.
Their laptop drives/Mini drives are Fujitsu and Seagate depending on price points I suppose (my Mini came with a Fujitsu and my Mom' MBP - purchased around the same time - came with a Seagate even though they are the same Capacity, specs, etc).
Most of Apple's ram comes from either Samsung or Micron (sold in the retail market as Crucial... but note that sometimes Crucial will ship ProMOS chips instead of Micron... not that it really matters).
Any HD will work fine. So long as you use cooler running FB-DIMMs I think everything will be fine thermally. I believe that early FB-DIMMs had a very hot controller chip and would pose problems, but that issue should be gone by now.