You can insert your ATM card and CIMB's Foreign Cash ATM will quote the exchange rate which you will have to confirm as OK before the transaction takes place.

I cannot remember the exact rate difference but I compared the rate offered by the CIMB FC ATM and Wawasan Sentosa's rate for US$ on the same day (sometime in late February 2011) and Wawasan's rate was definitely lower. Do note that that only US Dollar, Euro, Australian Dollar, Japanese Yen, Hong Kong Dollar, Thai Baht, Chinese Renminbi and Indonesian Rupiah is offered. See Press Release dated 25/8/2010 entitled "CIMB Bank Launches Southeast Asia’s First Foreign Cash ATM" here.