You should stick to PNGs when it comes to things like artwork and decals, not photos, as you said, they are larger in that respect, and take ages for anybody on a slow connection to load (Hint hint
).
If you don't want your images to pixelate, when saving them as a JPEG, just set the quality to 100%. While it makes it a larger file than normal, it does not compare to that of saving it to a PNG.
I'm not sure if you can do so in most programs, I know it works in Paint.NET and I think the Gimp as well. But I'm sure it applies for other image programs as well ('cept MS.Paint..). If you can't save to 100%, save one file to PNG if you want it to keep, and another to JPEG for sharing on the net.
~Amanda
