As mentioned above, there are a some things to take into consideration before scanning. Are they just line art? or are they shaded? or are they in color?
Line art = Scan as black and white
Shaded = Scan as greyscale or color then desaturate in Photoshop
Color = Scan in color
I try to always scan at 300dpi that way if you need it for print later, you don't have to rescan. You can always export it for web @ 72dpi.
If you scan it in Black and white or greyscale, bring it into photoshop and adjust the brightness and contrast (usually bump up both a little) and it will help to make the background completely white w/ no paper texture/fiber/etc. This way you can easily drop it onto a background by setting the inking properties of that layer to multiply.