MQ2MFilter (v1.1 edit: Don't use MQ2MFilter, in-game filtering command is sufficient for most users)
You can avoid using this plugin if you follow the excellent guide for /filter posted by Paldail: 
http://ezserveronline.com/forums/index.php?topic=2973.0

For users who wish to apply filters in custom configurations (various chars, installs, etc), you may wish to use MQ2MFilter. 

By an odd coincidence this plugin name uses a similar naming scheme as mine; however, this 
plugin was generously offered to us for use by the VIP's over at macroquest2.com. Please do 
not share or distribute or we'll all suffer :)

This plugin is used to add custom chat filtering. Unfortunately it doesn't filter 
serverside (obviously) as EQ filters do, but is still very useful for individuals.

/mfilter - toggles filtering active or inactive
/mfilter [on | off] - sets filtering active | inactive
/mfilter save - saves current filterset to filters.ini
/mfilter autosave - toggles automatic savings of any changes made to filtersets
/mfilter announce - toggles announcement of all filter entries upon first load of a filterset
/mfilter list [name] - lists all filter entries in "name" if provided, or all filter entries currently loaded if not provided
/mfilter addf what you want to filter - adds the supplied text as a new filter to the currently loaded filterset (do not use quotes unless they are part of the text you wish to filter, this is not a macro)
/mfilter remf # - removes filter # from the list of filters (use '/mfilter list' if you are unsure what number something is)
/mfilter load filterset [auto] - replaces the currently loaded filterset with the supplied filterset name. if you supply the auto parameter, the filterset will load automatically for that character in the future

/mfilter help - lists the above information