I am lifting this list from the Seattle Tech Startups discussion thread because this response from Ksenia Oustiougova is too good not to share broadly.  Ksenia runs a great company here in Seattle called lilipip! that does animated marketing videos.

Here is her list in response to the question of "what tools do you use to manage your personal workload."  Her answer is a great snapshot of the tools used to run a small business and an example of how any company can access a wide variety of really great products on-demand and at relatively low cost these days.

1. Project management – Basecamp
   
2. CRM – Batchbook
   
3. Documents (signing contracts) – EchoSign
   
4. Docs automatically stored if sent by fax via eFax
   
5. 
   Invoicing – Freshbooks
   
6. 
   Taxes – OutRight
   
7. 
   Operations (manual, overseas VPA's, etc) – Google Docs
8. 
   Scheduling – Google Calendar
9. 
   Voice – Google Voice
10. 
    Newsletter – MailChimp 
11. 
    Birthday/Thank you cards – Plaxo
    
12. 
    Conferencing – Skype
    
13. 
    Video management/hosting/tracking – Wistia
    
14. 
    Money transferring (anywhere in the world) – Xoom
    
15. 
    Sending huge files – DropBox and YouSendIt

This is a great list.  I think I'd add a few like a blogging platform (Typepad or WordPress), a wiki/collaboration space (like PBWorks), and various Twitter tools (like Tweetdeck & CoTweet) as well as the fact that you can address all your email needs with Google Apps.  Other adds would include marketing specific items like PRWeb for press releases, Jigsaw for lead generation/list building, and, of course, Gist for personal relationship management.