Hi Marcie,
There are so many good cameras available today - it really is buyer's choice to get the right mix of features/complexity/price. The Canon Rebel is a great camera - it's a digital SLR. I think Ken might use a Rebel - it's a bit more complicated than the S3 IS, but it gives you lots more options and flexibility. Lenses are sold separately because there are many different ways to use a true SLR and so lots of choices on the lenses.
As to the accessories for the S3 IS: it really depends on what you intend to do. Two things are essential: batteries and memory.
I would recommend getting the rechargeable batteries and charger. The camera will take regular AA batteries, but I find battery life is longer with the rechargeables. I always buy a fresh package of the non-rechargeable batteries before I go on a trip and wind up using them as I tend to take a lot of pictures.
Also, lots of memory cards. You can buy these almost anywhere. B&H prices are ok for these, especially with no sales tax and free shipping. I have 1GB and 512MB cards - I tend to use the highest resolution setting in the camera when taking shots - this allows lots of flexibility in post processing - especially if you want to do enlargements of your photos. WalMart typically has very good prices on memory cards, but if you live in a sales tax state you do pay the tax.
The camera can take video - it's not a substitute for a video camera but you can grab short movies. If you think you'll want to use that feature you need LOTS of memory - taking movies eats memory and draws down power. I generally turn the LCD screen off as this camera has an electronic view finder that shows you exactly what you are taking a picture of - this helps to conserve battery life.
The only other thing you'll need is a camera bag to hold the camera, spare batteries and extra memory cards. This is a very subjective choice - I would recommend going to a store with the camera and trying out various bags to see which one you like best. I actually would not recommend the Canon case - it's heavy and not big enough to carry enough batteries and memory cards for me.
The S3 IS has converter lenses available for both wide angle and telephoto use. I have and use both but that's because I like to indulge my inner photographer - they are not necessary. In fact, I often had to take off the telephoto lens because the animals were too close while we were in Singita! If you want to keep things simple, just use the 12x optical zoom that's built into the camera. You'll get beautiful pictures and we'll all get to follow along on your adventures.
Have fun shopping.
Mary Ellen