Most of mine are San Disk Class 4 4gb cards. I have a few others that seem to work fine. Lexar and something else.
I have problems with the Ultra 35 recognizing the cheaper quality SanDisc cards. Checked on a camera this Winter that never triggered and called Primos. They said they have been getting complaints about those cards. Switched to Sony and have had no more problems.
I use the cheapest ones I can find from walmart that are the minis with adapters. I like these so I can check the cards with my phone. (I have an android. Simply pop the back off, slide in the mini, download them to your phone, and replace the card). I think they are $10 each