In the latest move by a big bank to pick up some mortgage market share, National Australia Bank has launched a cash-back offer. Home-owners will get A$1000 cash if they refinance with NAB.NAB's "More Give Mortgages" campaign also includes a waiver of the $600 loan application fee and a discount of up to 15 per cent on mortgage protection insurance premiums. The offer runs from August 12 to September 30.Last week, Commonwealth Bank launched a campaign called "Fixed Rate Guarantee". The bank has promised to beat the advertised rates on the fixed mortgages of ANZ, NAB, Westpac, St George Bank, Bank of Melbourne and Bank SA.The offer covers fixed-rate terms for one to five years and runs until September 30. It is available to new and existing customers. Commonwealth Bank's three-year fixed rate is 4.89 per cent.Also last week, Westpac responded to the latest 25 basis point reduction in the cash rate by cutting its standard variable mortgage rate by 28 basis points.Among the big banks, NAB and ANZ have the lowest standard variable rate, at 5.88 per cent. Commonwealth Bank's rate is 5.9 per cent and Westpac's is 5.98 per cent.