Probably signature campaigns for the established members of this forum, The prices they offer in the services section are pretty good and reach 0,20-0,30 for high ranking members, the rate is lower in proportion to the lower status.
Yes if you are high ranked member and if you have joined some good campaign then you can make descent amount of bitcoins, and that is the easiest and safest way to grow your bitcoins especially for newbies.
Earning from signature campaign is a time consuming process though, you need to spend hours to earn few amount of bitcoins, I would suggest rather go for trading or gambling which can grow your bitcoins in a quick time.