Joining a new company in a new job is usually pretty exciting. Also nerve wracking but the unknown newness of it all is great. Well I think it is. Usually when we are joining a company we are on our best behaviour and out to impress. Some of us when we leave, are not. That's not to say that managers and companies always treat their employees well when they leave. They don't. Some examples I have seen:

• Being critical of an employee choosing to leave when obviously* said company is so good that how could anyone want to leave! I mean really.
• Lying about the reasons an employee is leaving the company because, again, how could anyone want to leave such a great company*
• Excluding the employee from all meetings that employee would normally attend during their notice period even though the employee did a good job during their service.
• "walking" an employee because they resigned. I understand this if the employee is in a sales role or going to a competitor, but in some cases it just seems, well, a bit not nice. In these cases the employee doesn't get to say goodbye to their peers and/or direct reports and I think that reflects badly on the company to the employees left.
• Attempting or actually withholding benefits that the employee is due.

* said with extreme sarcasm

Sometimes it's hard to leave some companies with dignity but I think you should. If you can. Here are some tips:

1. Un-subscribe from all your email lists - this includes shopping sites, hotel deals and holiday teaser type emails. The trouble with these lists is that once you have left your email will be forwarded to someone else in the company, for business continuity. If your email is filled with such emails the company may have wished you had left earlier. That's what personal email addresses are for. Only use your work email address for work related content.
2. Do not send one of those parting emails to the CEO or equivalent where you tell him/her and usually a number of  other senior people what you really thought about working for the company. Worse if your company hasn't shut this down, do not send an email to "all users". Most of us work in pretty small industries. This one will come back to bite you at some point.
3. Don't steal stuff. Customer lists, stationary, products or work that you have done including documents. If you want to take examples of your work, just ask. I have never been refused. Stealing some suff will just piss annoy your previous employer. Stealing some things will cause legal action to be taken against you.
4. Return all the company property in your possession.
5. Keep up the good work. If you can and if it's possible. Leave on a good note.