I had a friend just getting into digital photography and one of the first questions posed was "what size and type of memory card is best?" I told him that it didn't really matter, and after he looked at me blankly for a few moments I went on to explain. The size and type of memory card is less of the primary issue. The main issue is what you intend to use the card for. Just consider, you could take only tiny little images meant to appear online, and for that you could stick with the memory card that may have come for free with the camera.
Basically, this means that the first step in deciding about the right memory card is to understand your personal picture taking requirements and to then begin to understand the amount of resolution and/or compression you are going to use. For instance, you have an 8 Megapixel camera. That means your shots are going to have a lot of data, and that means that if you take an enormous number of images at any given time it could fill up a smaller memory quite fast. Thus, you don't want a 128MB or even a 256MB if you are someone using a lot of shots on a regular basis.
What we would say is that you want something like a 1 GB SanDisk memory card that works with the media slot for your camera. Remember that some cameras use different sizes, and it is always going to benefit you to know which is the right fit for your camera and your needs.
What about compact flash memory devices? These are really a killer in terms of storage space. For instance, the flash memory for a point and shoot camera (according to the PremierPhotographer website) gives the following:
If you want the largest range of options, purchase yourself a few 1 GB cards and keep track of what you are using them for. For instance, if you are doing a lot of shots of your pets or of the kids playing you are probably using the burst mode on the camera. Keep a single card for these shots and be sure to transfer them to a computer or storage often.
If you are using the RAW format instead of the JPG format, it is also imperative to keep track of things here too. The RAW file size is tremendous and you may run out of space very quickly.
What if you have an HD video option on the camera? The SanDisk website actually recommends that you purchase based on the amount of time that you need. For instance, they indicate that someone shooting in the fine mode is going to need 2GB for 20 minutes of shooting and 8GB if they want more than an hour.
One last question that a lot of people have about memory is if they need a different type or size based on the type of camera. For instance, will a DSLR need a larger or smaller disk than something like the mirrorless camera models just now entering the market? The reality is that you just need to choose based on the slot the camera offers and the type of photographic work you intend to do.