1D Mark III SD Card Size

I still have my 1D MkIII and love it, but want to get a few memory cards, SD probably. I have lots of 16 GB cards but wonder if anybody uses anything larger?

For SD/uSD, 2GB to 32GB belongs to the same category, designate as SDHC, so if you are OK with 16GB, you will for sure be OK with 32GB. >32GB, it is designated as SDXC. You can read the manual to see if the body supports SDXC

I've been using a 32gb card in my 1D3 without issue.

Yep, same here, 32GB CF and 32GB SD and sometimes a 64GB thumbdrive attached to my WFT-E2.
SanDisk Extreme 60MB/s UDMA 32GB CF-Card
SanDisk Ultra 50MB/S CF-Card
SanDisk Ultra 80MB/S SDHC I (10) SD-Card

The CF are my main storage.
In case I still don't have enough storage, I have the SDHC as a backup.
Most of the time 1 CF is sufficient.
(Why SanDisk? Because I happened to have a SanDisk Cardreader and never had any issue with this brand so no need to change)

Googled the pictures:

Sweet, thanks!

Feel the 1D3 love!