Tweetcaster - First Twitter Android App with Decent Filters

As opposed to Decency Filters :-)

I've only just started playing with the feature and amazingly, it isn't just the best implementation on a mobile, it's the best implementation anywhere.

Your can mute people, hashtags or keywords.

Tweetdeck, Seesmic et al should be ashamed of themselves for the lack of progress in this area on the desktop.

Speaking of which there is a Chrome plugin for Twitter which does filtering called Slipstream. I tried it out but it only allows one exact word/phrase per filter and only works on twitter.com. Worth a look tho if that's all you need.