Sandisk is good one. It has to be at least Class 10. The Sandisk Extreme is pretty good. It's fast and it doesn't cost a lot. But if it is still a little expensive, you can use the Ultra lineup from Sandisk (a bit cheaper but still good for your camera). You don't need to spend $ on the Extreme Pro line up.
In short, any card with write speed faster than 20MB/s is good for both still and video. Personally, I like Sandisk and Lexar.
Do you shoot video or mostly stills? I don't think there's a lot of difference in burst speed (if shooting RAW) by card speed, providing that you're using a modern speed card. The super fast cards (90+ mbps) are a waste of money, IMHO. I use Sandisk Ultra and Extreme speed cards, and I can't really tell a difference. I do buy name brand though (Sandisk and Lexar), the little bit of extra money is worth the cost. I've never had a SD card fail, and I don't care to.
Movie may be a different story. I know people who shoot a lot of movie usually use super fast cards.
Edit: Every time I finish typing a response and hit post I find that either HSBN or Cicopo has beat me to it.
Definitely buy quality cards and stay away from cheap and mediocre ones. I've used Sandisk for years and have not had any issues with them (knock on wood). Currently use Extreme and Extreme Pro in dSLRs, and Extreme in Powershots. I do not shoot video, except maybe an occasion casual video from a Powershot.
Personally I like smaller capacity cards like 16 gigs as opposed to larger capacity cards. I prefer to put my eggs in multiple baskets as opposed to one giant basket just to be safe. Make sure you always format your cards from your camera before use.
B&H always seems to have great prices.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
04/20/2023: New firmware version 1.4.1 is available for EOS R3
03/30/2023: New firmware updates are available.
2/07/2023: New product announcements!EOS R8 EOS R50RF-S55-210mm F5-7.1 IS STMRF24-50mm F4.5-6.3 IS STMRF15-30mm F4.5-6.3 IS STM