Surprisingly, you could save a lot of money by making your mortgage repayments weekly or fortnightly, instead of monthly. One reason for this is that interest is calculated daily. Working from this, if you make your repayments fortnightly (instead of monthly) you are also making payments more frequently, thus reducing the interest you will end up paying on the loan.
The other reason fortnightly (or weekly) repayments could save you money in the long run is that there are 12 months in a year, but 26 fortnights. If there are 4 weeks in a month, then 26 fortnights is actually the equivalent of 13 months. This means that you are annually paying more towards your mortgage and thus, paying it off quicker and reducing your interest.