Rackspace Cloud / Linode (we'll be moving everything to Linode eventually... the Rackspace thing is a legacy of their Slicehost acquisition)
SugarCRM (self-hosted)
Mediawiki (self-hosted)
Bugzilla (self-hosted)
Hoovers.com
LinkedIn
Google Apps (mainly GMail)
Apache httpd
and some internal tools we developed ourselves, like our competitive intelligence tracker, codenamed FUCIT (Fogbeam Universal Competitive Intelligence Tool) and a product dashboard tool I'm working on now.
Google drive (a lot of stuff was done in it)
Google keep (really, I've deleted evernote as I like simple in use tools)
Pocket (not to forget a lot of helpful links)
Gmail
Buzzsumo (great tool but I've learned about lately. All stuff was done before)
Webflow (to create landing page)
Adobe Illustrator (to make all design)
It seems that my list is too short. But I think that you have to concentrate on your startup idea and not the searching of 'right' tools. If you really need them you can read here: http://www.quora.com/Startup-Founders-and-Entrepreneurs/What...