Now there are digital cameras with option for extendable memory. Even the internal memory is also sufficient. But there are some cameras with you get free memory card to extend memory.
There are cameras for canon. kodak, casio which are the best and I think 3 – 6 mega pixel cameras are sufficient according to ur need if you want more go for 7.1 mega pixel it is more than sufficient

The Kodak Easyshare range are quite popular and I have one too. It’s 5 mega-pixel, so with a 2 GB memory card in, I can take over 1200 pictures at the best quality.
My brother has an Olympus and they’re good too.

While there are some really BAD cameras being sold that promise to be MP3 players, webcams, have a huge digital zoom and are "focus free", just about any camera listed on this website will be a good camera for its price.

http://www.depreview.com

The P&S cameras use SD memory cards (all but three), xD cards (Olympus and some Fujifilm) and Memory Sticks (Sony). Choose a camera that uses SD memory cards, since they are the easiest to find and cost the least per GB.

Buy one long before you go on vacation and learn to use it first. Waiting to learn to use cameras while traveling is usually a disaster.