JL - I chose the 256MB SanDisk Ultra at about $149.00. I will end up with a pocket full of these before long. The 512MB Ultra is around $500 each, and I have heard that the 1GB 'MicroDrive' is fragile, especially if dropped. They are around $260.00 I think.
There are several brands of 'Ultra' available and prices vary from day to day. No problems with the SanDisk and it is detectably quicker saving than the non Ultra.
On the 256MB Ultra, with settings 'Fine / Medium' I get (133) images, 'Raw' (25). I hope this answers your questions JL. Attached is my D100 snapshot of some Koi at a local garden walk.