The size of the card depends on the operating system you have on your phone:
BlackBerry Device Software 4.2.0 Up to 2 GB
BlackBerry Device Software 4.2.1 Up to 4 GB
BlackBerry Device Software 4.2.2 Up to 4 GB
BlackBerry Device Software 4.3.0 Up to 8 GB
BlackBerry Device Software 4.5.0 Up to 8 GB
BlackBerry Device Software 4.5.0.81 and later Up to 16 GB
BlackBerry Device Software 4.6.0 and later Up to 32 GB
I find Sandisk reliable. As for size, well, I would suggest the largest you can afford if you want a lot of music and/or videos and photographs. Plus you can store any other documents or files on it you want (I keep a copy of the UNinstalled Desktop Manager on it as well as a copy of my backup data - in case I need to reinstall or fix things when away from home). I know 8gigs works on the latest OS. I'm not sure of 16gigs but that may be a bit much (G)
Ron if you don't have a media card already installed in your device you need to do so. If you are out of device memory you could start experiencing all types of problems from texts deleting to slow response time, etc you name it. Also once you get that media card you will need to move all of your media over to the media card to help increase your file free memory.