If you always plan and compose your pictures perfectly, you don't need a whole lot of pixels. These days, I'd say that 5 MP or even 4 MP is fine for the average snapshooter and this can be obtained without unreasonable expense. If you want to allow for cropping, which means enlarging only a portion of your image, the more pixels the better.
Imagine taking a scenic view and then noticing that the middle 20% of the photo would make an even better picture. Suppose you take a picture of a whole group of people and Aunt Clara really, really looks great in the picture, but everyone else looks lousy. If you have the pixels to work with, you can still make a decent print of Aunt Clara that she would be happy to have. If you buy an 8-to-10 MP camera and don't want to TAKE large photos, you can always set the camera to a lower file size. You can never go the other direction, though. Unless the cost is a major issue, buy the camera with more pixels. You will never be sorry that you did, but you might one day be sorry that you didn't.
I have a few photos on Flickr to include in a discussion on how many pixels are enough. Go to my page at http://www.flickr.com/photos/samfeinstein/tags/pixels/ Some of the pictures are from a 4 MP or even 3 MP camera, showing you what you might expect without any cropping. I think they are quite acceptable. Some of the pictures are from a 10 MP camera (the swan and the pansies), showing the value of having those large images so that you can crop a smaller image out of the original picture and still end up with a satisfactory image. There is one VGA picture, just to show what you could expect from 640 x 480 pixels - not much.
Ken Rockwell has an interesting article on pixels and the pixel wars: http://www.kenrockwell.com/tech/mpmyth.htm
Having said all that, though, pixels are not the only measure of image quality. The sensor size is important as well as the image processing software included in the camera. (See http://www.flickr.com/photos/7189769@N04/476181751/
You need to read reviews if you want a critical understanding of image quality for particular cameras. Try http://www.dpreview.com/reviews/ for more information on the cameras you are considering. Pixels are not the decision maker, but they are the tie breaker, so go for the higher pixel count.
You can go there and click on "Buying Guide" and then "Features Search" to specify how many pixels you want to look at.
You can also go to http://www.steves-digicams.com/default.htm and click on "Our reviews," where you will find catagories of cameras arranged by pixel count.