As usual the trick is to get inspired and not slavishly follow any particular implementation. Due to each site having differences in design and purpose, the only way is to do continuous a/b testing.

http://visualwebsiteoptimizer.com/split-testing-blog/tag/cal...

http://www.campaignmonitor.com/blog/post/3073/a-b-testing-th...

http://thinkvitamin.com/web-apps/how-to-increase-sign-ups-by...