#1. "RE: Memory card compatablility with D3100" In response to Reply # 0
That's a lot of memory card considering I got the D3100 body itself for cheaper than that! Yes, it should be compatible, but from a practical perspective, you're better off breaking up your cards into smaller capacities to guard against a single card failure.
#2. "RE: Memory card compatablility with D3100" In response to Reply # 0
I am new to the D3100. I plan to do HD video with this camera (if it works well and easily enough). I want to be able to get at least 3 hours of video on one memory card. What memory cards would you suggest?
#3. "RE: Memory card compatablility with D3100" In response to Reply # 2
You should be fine with the 128GB. Just be aware that all still cameras doubling as video have an arbitrary 20-30 minute limit per clip. That's to prevent them from being taxed at the higher "dedicated videocamera" tariff rate when they're imported into certain countries.