I was thinking of buying a Canon Powershot digital camera. What accessories or parts would I NEED to buy in order to use it? Ex: flash memory, etc. Also, will any flash memory card work with any digital camera? Thank you in advance for your answers.

Which model are you interested in, we all want to know?   
Fred said:
I'm not sure if I'm more experienced than Fred  but an external flash can be useful, they are much more powerful than the built-in flash on a compact camera, indeed, any camera including DSLR's.
I'm not sure if all Powershot models have a flash hot shoe, so make sure the model you choose has one, even if you don't buy a flash gun straight away.
My advise is to buy the most powerful flash gun you can afford, obviously it does not want to be too top heavy on a compact camera, but there are ways of solving that - a flash bracket that is secured by the tripod socket - but that is another story 

The essential accessory is a carrying case or bag to protect your valuable asset. Make sure it has capacity for spare batteries (oh yes, don't forget those), cards and possibly a flash unit.

I must say it's good to hear someone talking about a compact camera, rather than all the "heavy" stuff that many of the guys & gals here use. Compact digital cameras have done much to re-invigorate photography for everyone, rather like when the old Box Brownie was introduced.
Fred will remember those 

Terry.

If you do landscapes you can add a polarizer filter.
http://www.luminous-landscape.com/tutorials/polarizers.shtml

Well, the best I can do is second the other suggestions and add my reasons why.

Spare battery; its a horrible experience to run out of power when you need it.

Extra cards;  I use multiple smaller cards as card error can happen and recovery software is not all that reliable.  If you do lose a small cardful of info at least you don't lose everything.

Filter; if you scratch a permanently mounted lens the camera is toast.

External flash only if the camera has a hot shoe and e-TTL;  The flash to lens angle with in-camera flash is too small and will cause red eye, specular highlighs, and real bad pre-flash eye-blink.  External flash, especially with a coiled extension cord, gives you many more options like; adding a diffuser and hand holding the flash in an optimal position for close ups, a greatly increased guide number, quick flash compensation adjustments, flash color filter additions for effects and mixed lighting...I can do this all day...

...anyways, Powershot cameras are point and shoot cameras designed for convenience and really do not even need accessories, so you could also enjoy this type of camera as is out-of-the-box too...so...Happy Shooting with your new camera

Yup, PhotoRecovery is pretty good software suggestion Seth.  Not all recovery software is the same, as I'm told by our IT guy.

Just a thought, and maybe I'm too cautious, but different situations could place different limitations on recovery. Sometimes all the files won't come back perfect making it tough to take never fails to the bank.  Its always up to the user, but maybe an ounce of prevention isn't too bad way to go.