I have recently been doing the necessary background reading toward the selection and use of filters. It's still a work in progress, but I have started amassing a list of resources/pages/threads that may be of use here, some no doubt more than others. You may as well get the benefit of my hours of searching.
Some of the pages/threads below are aimed at astrophotography, but still useful (and you might have to read the whole thread to find that one really useful post). At this stage, I was mostly aiming at understanding the uses of broadband (a.k.a. "light pollution") vs narrowband (a.k.a. "nebula") filters, although it appears some would say that a "nebula" filter makes a better "light pollution" filter and that a "light pollution" filter isn't worth the bother; I've yet to make up my mind.
You should start here:
http://www.iceinspace.com.au/63-680-0-0-1-0.html
And then continue:
http://www.karmalimbo.com/aro/filters/filters-intro.htm
http://www.karmalimbo.com/aro/filters/filters-findD.htm
http://www.karmalimbo.com/aro/filters/filters-useD.htm
http://www.samirkharusi.net/filters.html
http://www.cloudynights.com/item.php...d=63&pr=2x9x42
http://www.cloudynights.com/ubbarchi...t=1&PHPSESSID=
http://www.cloudynights.com/ubbarchi...7/Main/1176970
http://stargazerslounge.com/topic/40...-transmission/
http://stargazerslounge.com/topic/56...ters-the-same/
http://stargazerslounge.com/topic/50...-2-lpr-filter/
http://stargazerslounge.com/topic/15...hc-v-cls-clip/
That was only one night's worth of searching, so there'll be more at some stage.