As source control: why not a distributed system, like git (if you are not using Windows), Mercurial or Bazaar?
For bug tracking, I would go on Trac - it has also an integrated Wiki, that is always useful for project documentation.
As for build management, you could go on cruise control, or ant - I am not really expert on this side.
However, there is something you should really take into consideration: the main issue for distributed teams is not the toolset, is communication.
This is even more important in an "agile" setup, as suggested by your tag.
The best mitigation I have ever seen for this issue is videoconferencing. It is very effective for enhancing communication bandwidth in distributed teams, and with GTalk and Skype is now really inexpensive.
