Hi Garry, no, filters are not necessary, but they can help. In a light polluted sky the can be the only way to bring out detail or even see them. At a dark site filters help tone down the background or improve contrast.
Which filter is best depends on what you are chasing, where you are observing from, & on the size of instrument you are using. Just on the last point some filters transmit so little light that unless your scope is large enough there is just not enough going through to actually see anything!
Before you spend money on filters, do some reading. There is a good article by John Brambury about them:
http://www.iceinspace.com.au/forum/s...ad.php?t=89413
I also suggest you go to a star party where you can see these things in use & even get to try them out in your scope BEFORE you buy. You can burn a lot of dosh with filters!