Currently I'm using TikiWiki (http://tiki-wiki.org) for keeping our designs and todo list. But after reading this:

How Funcom Squashed Bugs With Bugzilla (http://www.gamasutra.com/features/20031120/hansen_01.shtml)

I've decided that I really want something like it. Really like the way they can estimate and prioritize tasks and know if they will be able to hit milestones. Also the reporting stuff.

Not sure if its overkill for a small 3 person team though, but would be real nice to have in place for the future.

Anyone have any other similiar/good opensource collabration tools with this kind of functionality?

I'm on the look out for the same thing too.
I am using Perforce (2 user, free version, highly recommended for indies) as my source control system and it has a poor defect tracking facility. They let other solutions integrate (TestTrack Pro, Bugzilla etc) but Bugzilla is web-based and I dont prefer web-based and TestTrack Pro is commercial and pricey.

For now I'm using the Perforce Job facility to track bugs but its not that intuitive.

This nice site
http://www.opensourcecms.com/
allows you to test various open source content management systems before you download them. Maybe you'll strike gold?