- Dropbox - for assets, design documents, you can also store here todo lists, assets list, some other project files, etc.
- SVN/Github/Bitbucket - for programmers specifically as for example Visual Studio and Dropbox seem to hate each other. When you and others work on the same project opened several times on Dropbox, it will start to create some crappy database files or other shit that takes quite a lot of space. It's just irritating.
- Forums - can work the same way as Dropbox, surely brings better organization of files and may look better but isn't so convenient, Dropbox is much faster to use, though we still use forums for some development-related things.
- Wiki - project documentation, not every project needs it though, for some forums work just as fine
- Skype/MSN - for chatting & conferences.
- Google Docs - sharing documents, with the possibility of real-time co-writing is surely something that could be useful.
Indie tutorial: Organizing your work as a team