This is an email from a friend of mine who surrendered his PR in case I need to do it too. I think its exactly what you need:
Go down to SiR/ICA (or whatever they call themselves at this moment) and inform the information counter that you want to cancel your PR. Be sure to take your passport, IC and the entry permit. They will take you into an interview room. Don't worry, no one will interview you. A pleasant officer will let you ask you if you had any dependant PRs (no). She will inform that once PR is cancelled, a social visit visa will be issued for a month and that will help you finish off all work and leave Singapore. She will take back your IC and entry permit and cancel the re-entry permt. Then she will stamp a 1 month social visit from that day and give you one half of the disembarkation form/card. She will also give you a letter stating that ICA has accepted your PR cancellation request and that you have returned the IC as well as the entry permit. Keep this letter safely.
To the CPF board
Take the letter you got from ICA and go down to the CPF board. They will use this letter to close your CPF account. For quicker processing, pass them a bank account number in Singapore to remit your CPF amount. If I am not mistaken, they can also provide demand drafts (issued in your name only) etc. and send it to your permanent address overseas, if you cant wait in Singapore for the money to arrive in the bank. Bring along some document showing that you indeed have that account. One of the month's statement of account will do. Else you will be asked to sign an indemption form. They will need about 10 working days (i.e excluding Sunday and public holidays) to get the money into your account. I got the amount in my DBS account on the 9th day. If your employer has to pay any more CPF money to you, they will give you a letter instructing your company that you have closed your CPF account and that any amount (employer or employee contribution) still due to you should be paid to you directly. Take this letter and pass it to your company. They should then be able to give you the money directly. They will have to fill up the reverse section of that letter and send it back to CPF board.
Go down to IRAS and get an IR21 form. This form is to be filled when someone is permanently leaving Singapore and the taxes have to be settled. Get the company to fill it for you and return it to IRAS. Companies that use e-filing can fill the IR21 form online. Ask your employer if this can be done, so that you don't have to run to IRAS twice. IRAS will then compute the tax that you should be paying. Pay it. Note that the CPF board will ask IRAS for an "OK" with respect to your taxes before they credit the CPF money to you. If you have not filled in the IR21 form and not filed your taxes, IRAS will not give the green light to CPF board. If you are rushing (as I was), do let the IRAS officer know your emergency. They may help you by expediting the process. Ofcourse for this, e-filing will not work. Person-to-person contact works wonders in these cases. They took about 5 working days in my case.
That should cover everything that you will need to do in a normal case when dealing with ICA, IRAS and CPF board.