The first question you need to answer is whether you want a copyleft license[1], that requires all derivative works to be open sourced as well, or a more liberal license that allows one to use your code in a proprietary application.
If you are OK with a liberal license you probably want to pick either the BSD[2] or MIT[3] license. For example, Django uses a BSD license.
If you want a copyleft license you probably want to use GPL[4] or LGPL[5]