KOLAB - kolab.org
The main site for all the documentation, packages and news around Kolab
Regfish - www.regfish.net
If you are looking for a powerful DynDNS service, regfish is the right site for you.
MailJet - www.mailjet.com
Sending mails from a dynamic IP is not possible for most of the server so you need a relay with a static IP. MailJet is cheap and free of charge if you send less than 200 mails per day.
StartSSL - www.startssl.com
If you want to secure your services you can use selfsigned certificates or those certificates from StartSSL which are free of charge