Differences between 咱们 and 我们？ 我们 [wǒmen] and 咱们 [zánmen] both means: we, but when I should use 咱们， 我们？

What is the difference?
我们 can be used both formally and colloquially across all Chinese speaking regions, while 咱们 appears more in spoken language and more in Northern China. 
我们 may or may not include the listener, depending on the context, while 咱们 almost always includes the listener. 
Although 咱们 includes both parties, there can be a strong or even exclusive focus on one party, either the speaker (e.g. 瞧咱们的 = "we'll show you how it's done") or the listener (e.g. 咱们不怕 = "let us not be afraid"). This type of usage is very common in Northern China but can be quite unfamiliar/unnatural to other Chinese speaking regions.


References:

[1] http://www.chiculture.net/0615/html/d16/0615d16.html

[2] http://www.fed.cuhk.edu.hk/~pth/pth_passage01.php?passage=99