All that's really required to leave a job is to let your management know in writing that you are going to be resigning as of a particular date. However, there are a few things that you should check up on to make sure that you're scrupulously regarding all the procedures and laws that apply, and to make sure that you're entitled to everything you think you are. There are also preparations you can undertake to make your leaving as smooth as possible and to minimize inconvenience for yourself and for your employer.
Although it's doubtful that a resignation ever comes as a total surprise, your employer is probably not instantly ready to cope with your leaving. Mind you, there are times you know that you're being eased out, for whatever reason: meetings you're not invited to, memos that leave your name off the carbon-copy-list, generally you're being bypassed; in such a case you will want to pre-empt the situation and resign before you're chopped. Even then you're making the decision, not the company. Unless they plan to be rid of you, they can't be taking very obvious measures to replace you because then everybody would be in on it, probably making the situation less pleasant all around.
So for your own protection and for as much good will as possible, take a few steps in advance. Take home personal items that you have at your desk, cubicle, or office. These days, it's not unknown for someone to be escorted firmly out the instant they present their letter - you might not have time to retrieve your personal stuff! If you feel protective coloration is needed, bring an old photo of your family, one that you won't miss, and leave it on your desk to replace anything else that was there. You really shouldn't have used the company's facilities for your own use - such as your own files on your office PC - but if you have, e-mail them to yourself or otherwise save them, and take them off the company's equipment! If you've sent out any regrettable e-mails, you may be stuck, because "Sarbane-Oxley" and other regulations these days require the company to keep copies of all messages for later reference; at least zap them from your outbox.
Make an effort to bring all your projects as far up-to-date as you can. There's no point in sticking someone else with unnecessary work, when they take over yours, although of course you may not be able to avoid that. If you're asked to take on something large and urgent you'll have to do some creative squirming; if you can't refuse at least put some time in on it. You do want to maximize the goodwill towards you, remember.
Finally, do a bit of homework. Find out what the proper period required for giving your notice is. Usually, it's two weeks, but your contract or employment agreement or laws may specify otherwise. Visit H/R and find out the regs on dropping out of company benefit plans, and how to maximise what you can walk away with. (You can quite correctly give as your reason that you're doing some financial planning.) See if your employment situation requires you to observe "non-competition" regulations; sometimes known as "yellow-dog" clauses, these forbid you from taking up a position or line of work which would compete with your present employer. And it may be the case that you can't even apply any know-how you've acquired on this job. All these are things that have come up when people have changed jobs. It's best to consult a job-regulations expert if you have any doubts at all. Such resources should be available at the municipal or government level.
Leaving a job is a part of employment, and as such it deserves the same sort of preparation as most other changes in life.
Index of Resignation Letter Examples