There is a great service (still in Beta), called eintelli.  It's an online tool for creating proposals.  I've been looking for decent tool to use for a while, and early this year wrote about proposal collaboration software, Zapproved. Zapproved is an ideal tool for seeking proposal approval (hence the name), however, eintelli is the ideal tool for writing your proposal from scratch.

Eintelli, is one of the few vendors offering an online tool for proposal creation, at least from my research anyway.  I found a lot of outdated software vendors that offered proposal software, however, I'm sure you can relate, purchasing software has lost it's appeal! 

The idea of eintelli, is that you can create your proposal online, then send a link to your recipient to review, or you can export as a PDF.  The PDF comes formatted (as a proposal should look), and the table of contents is automatically created.  

Features for creating your proposal online

Create Proposal 

Create media rich branded proposals, that can be stored online and accessed from anywhere

Publish your proposal

Allow your recipients to view your proposal online, plus add a level of security by opting for password protection

Proposal Intelligence

Built in business intelligence; tells you who has viewed & for how long

Proposal Templates

Create & save proposal templates that are specific to a product or industry your pursuing

Real Time Collaboration

You can invite other users to collaborate on proposals.  The experience is in real time, so you can see your colleagues typing! 

There is a host of other features, that support optimized printing of your proposal, request approval, feedback & more.  

Overall, this is a very impressive online tool for creating proposals.  At the moment, it is in Beta & offered for free, so you can't go wrong!