Getting at the_content before it's had extra tags added

I've just discovered an interesting snafu in my content-processing plug-in. I built a filter for the_content, but I'm finding that the string passed from the_content isn't the same as the actual content stored for the post in the database. In particular, paragraph tags have been added before I get to the_content to add my own processing.

Is there a way to intercept post content prior to display and prior to when WordPress adds various tags?