• Grandcentral - www.grandcentral.com: This allows you to have a phone number that you can use for everybody. Then you can easily sort out who from your contact list can reach and how. Plus all voicemails are accessible through the web, so it is very convenient when you travel.
• Gizmo project - http://gizmoproject.com/ : this is a Skype equivalent, I like it better because it takes less resources on my computer, but you can use Skype as well if it works better for you. You can use this software to call anybody with very cheap rates from your computer. Can be a nice extension to a regular phone. Quality is not always perfect, so not recommended to use with customers
• Lingo: www.lingo.com - this is what I use for my regular phone line. Very good quality of the calls, very convenient. It just works and it is cheaper than a regular phone line.
• Netcipia: this is a wiki/blog www.netcipia.com : you can sign up and create a place (hautecouture.netcipia.net) and then you can invite anybody you want to include. This is a wiki, so anybody can edit. And you can decide that some of the pages can be public (if you want to create a blog for exemple). I use this to coordinate projects with people. An alternate solution to do this (not as good from a technical prospective but more features at this point) is Socialtext - www.socialtext.net - OR pbwiki - www.pbwiki.com
• Netvibes - www.netvibes.com : if you are going to use Netcipia, you need a tool to stay aware of changes to the Netcipia place, and you can use Netvibes for this. You subscribe to the RSS feed from your Netcipia place, and you can use Netvibes to monitor what is happening with the place, so that you go there only when there is something new to look at or when you need to edit the place.
• Google: I use Gmail. but also google docs to share docs between people. They have a google for small business that is very convenient if you want to manage a few users (email, calendar, docs) within a given domain name.

Actually the best of all is to get your domain name managed by Google so that you can benefit from all this functionality through Google Apps, which is all integrated.

• Yammer - www.yammer.com - a virtual water cooler very useful to allow people to stay in touch with each other