I think that this quite recent article (June 2014) about the "Sign Up" button can help: the author changed the “Sign Up” button to “Try it Free” and clicks increased by 212% (more data in the article).
His thesis is that the standard "Sign Up" buttons don't work because "they ask for blind commitment" and "do not offer any value".
Visitors also "see common elements repeated on many sites" and "they begin unconsciously ignoring those elements (aka “habituation”)".
Therefore he suggests to:
- Tie it (the call to action) to your product. If you have a SaaS for trading bitcoins: “Start Trading Bitcoins.” If you have a
marketplace for artists: “Start Selling Art.” This helps prevent the
button from being
- Give, don’t take. “Get Access” and “Sign Up” both lead
to the same thing, but one makes the visitor feel they’re getting
something, while the other doesn’t.
- Compell people to act. Use
action verbs such as get, start, and try.
Of course there are many variables we need to consider (e.g., about your website's users, the business model, etc), but I think it's worth having a look at it.
And testing is, as always, key.