2.1 megapixels is usually fine. This will allow you to take pictures at 1600x1200 resolution, which is easily good enough for 4x6 prints.

2.1 is very good; almost as good as 35 mm film when you enlarge to 8 x 10. 3 megapixels and up is for professionals and portrait photographers.

The answer is that it depends. If you only want to make small prints (4x6 or 5x7) or you are only interested in sending the images over email or displaying them on the internet, then 2 megapixels will do just fine. You'll probably be good up to 8x10 with a 3 megapixel camera. A 4 megapixel camera will get you okay prints up to poster sized (20x30). It does depend on the printers that you use. I recommend www.smugmug.com for online printing. The thing to consider is that if you are planning on cropping your pictures in any way, you will definitely have problems with those image sizes. Also if you are only going to be displaying your images on the web or sending them via email, 3 and 4 megapixels will be much too large. In that case you'd end up resizing every image you take anyhow so why go that route? You'd be better off with a 2 megapixel camera. If on the other hand you are planning on taking high quality shots and printing them large (or very large) after some cropping you should consider 7 megapixels and beyond (depending on how big and how much cropping you do).

This is an update, since the previous answer is over two years old... Current cameras as of this writing (excluding phones and other gadgets) are typically in the 4+ range. A 3.5M camera will give reasonably nice results for an 8x10 (units in inches). A 6M camera can push out to 13x19. Sensors that are larger than about 6M will start to push the limits of the lenses attached; a compact point'n'shoot may not look as good as an SLR in actual quality, though it will have enough resolution that pixels won't show up in larger prints.

The answer depends a lot on what you want to do with the pictures. A 35mm film camera’s 200 ASA negative is about equivalent to a 35 mb digital camera, in resolution size and no common consumer cameras are that good. As of March 2006 there are many that capture up to 8 mp. However it is awkward to send pictures over 1 mp to people via emails, and few web sites contain images that exceed that size so if you want a camera that takes pictures you can send to people in emails, 1 and 2 mp cameras would work. Now you ask why have more? Many people crop their pictures and if you want to be able to enlarge any part of the picture, such as one person in a group, you can’t do it and still have decent detail quality, unless the entire picture is taken at a much higher resolution. The same applies if you intend to use the digital zoom capabilities of any camera. When you digitally zoom in to any picture you loose overall image quality very quickly. Zooming into the upper left quarter of a picture reduces the image detail 4 times, (doing so on a 4 mp camera would give you a 1 mp image). The many popular cameras have 3 or more mega pixels and 3 or more times optical zooms. Unless you intend to create prints over 8 ½ x 11 or are real serious about detail that you can not print on most home or office color printers, 3 mp with 3 times Optical Zooms will work just fine for you. As a last note, today mega pixels are probably far less important to most people than other features such as the optical zoom range, the effective flash range, the speed of the lens and the availability and cost for the batteries. Lots of new cameras have plenty of mega pixels but many can’t take good flash pictures across a room.

4 would be fine.... http://www.picturedeland.com

If you think the 8 x 10 prints from a 2.1 mp camera are almost as good as 35mm film you probably don't know how sharp and precise film prints really can be if the processor takes the time to focus the image. If the neg is sharp and clear, (not out of focus or blurred), you would need a magnifying glass to see all the detail it could transfer to an 8 x 10 print. To give you a good idea, a good scanner must be capable of scanning at at least 48,000 dpi in order to produce decent image quality from a 35 mm neg, or it looses a lot of the detail. No common digital camera gives you 48,000 lines of optical resolution in a picture, or even comes close at this time. Then again a normal TV screen is 540 x 480, so good quality is really all related to what you are happy with and that depends on what you want to do with the pictures you shoot. Since few people want to receive pictures over 1 mb in their email, and few web sites contain images that large, many people don't need cameras that shoot those real high resolution pictures except to impress their friends.

almost all regular cameras offers decent megapixel levels, now if you are going on vacation I'd think in getting more zoom. 5X zoom plus +3 MP is a good combination.

If you are looking for a camera for casual use, you shouldn't be concerned about megapixels. Almost all camera's between 100 and 300 dollars will give you good resolution. Instead, you should be more focused on ease of use. For casual camera, you should probably buy more of a "point and shoot" camera, rather than a very complicated one with a lot of settings you will never use.