Twitter, the subject of endless business model speculation, added another weapon to the arsenal today – house advertisements on the home page when you’re logged in, and some search results.

The advertisements currently only link internally to Twitter Search or the Twitter Widget. But it isn’t much of a stretch to assume they’re testing the units for possible third party advertisements in the future. Twitter Japan, which launched a year ago, has included display ads from the beginning.

Last summer Twitter CEO Evan Williams said he thought Twitter’s strongest revenue potential would come from charging for commercial use by brands. But it’s clear that the company will experiment with a number of different potential streams – we think Twitter search has tremendous revenue opportunity.