You might want to look at this other thread on IIS:
http://www.iceinspace.com.au/forum/s...d.php?t=117915
I spend a little time explaining the various nebula filters.
If you get just one, it should be a narrowband filter that passes H-Beta, and the 2 O-III lines (486nm, 496nm, 501nm).
Good examples: Lumicon UHC, Orion Ultrablock, DGM NPB, Thousand Oaks LP-2
A beginner might want a neutral density filter for the Moon, a red filter (dark markings on Mars), a yellow filter (Moon, dust storms on Mars, Saturn's rings), and a blue filter (Venus, Jupiter, Saturn's disk, Mars' ice caps and clouds), but they aren't essential. A good narrowband nebula filter, on the other hand, is amazing in the difference it can show--even in heavily light-polluted skies.