I need to get a memory card for a Nikon D90 camera. I think it needs to be class 6 or better so that camera is not slowed down by memory access. Are there any other things to consider when getting memory for a camera? What is a reasonable size to get?
Well, I use a 15Mb/s Sandisk Ultra 16Gb (which is only a class 4 I believe) and I have no issues.
Burst mode and bracketing can have some issues while waiting for sync from internal memory, but I have yet to find a shot missing when doing an import.
If you are wanting consecutive high burst frames, then yes, you might want a faster card but then again, I believe the body is going to limit you and thats where the D300 and higher make some grounds.
So, you already know it has to be fast enough. When looking at speeds, make sure the write speed is fast enough. Some manufacturers quote a very high number of read speed, which does not help much with the camera.
Reliability should be your next concern. The best brands such as Sandisk, Lexar and Kingston back their cards with a lifetime warranty, showing their trust in their product. Be careful, these brands offer different classes of cards. For Sandisk, you are looking for a card that is black or red, not blue. Lexar labels the high-end ones with 'Professional'.
Size is a more personal choice but if you plan on doing video regularly, you'll need something rather big. Based on your shooting and workflow, you may want to have a card that's big enough for at least an entire day of shooting.
However reliable these things are you should still download and backup your pictures regularly, don't wait for months until you card fills up just because you bought a huge card.