I typically use high concentrations of each oligo (1mM) in a buffer with about 100mM salt (I use NEBuffer 3).  I drop the tube containing the oligo/salt mix into boiling water (at least 200 ml of water in a larger beaker on a hot plate).  I then simply turn the heat off.  This allows the solution to very slowly cool.  It can take couple of hours for the water to reach room temperature, but I have not found a strategy that provides for a higher percentage of the oligos to have annealed. 

In the future, consider ordering one full length oligo and one short oligo.  The short oligo is allowed to anneal to one end of the longer oligo and then you use your favorite polymerase to fill-in the remaining single stranded portion.  In my hands, this is the very best method for longer duplexes.  The fill-in method is particularly useful when their are potential secondary structure issues.

Just to clarify.....you have complimentary oligos which you want to join to form a single dsDNA fragment of 61 bp?  Is that correct?  If so just mix at a 1:1 molar ratio, heat to 95 deg C and allow to cool.  If there's no strong secondary structure they will probably anneal at room temperature, the heating step will ensure (unless of course the sequence has repeats) the duplexes are formed correctly

I typically use high concentrations of each oligo (1mM) in a buffer with about 100mM salt (I use NEBuffer 3).  I drop the tube containing the oligo/salt mix into boiling water (at least 200 ml of water in a larger beaker on a hot plate).  I then simply turn the heat off.  This allows the solution to very slowly cool.  It can take couple of hours for the water to reach room temperature, but I have not found a strategy that provides for a higher percentage of the oligos to have annealed. 

In the future, consider ordering one full length oligo and one short oligo.  The short oligo is allowed to anneal to one end of the longer oligo and then you use your favorite polymerase to fill-in the remaining single stranded portion.  In my hands, this is the very best method for longer duplexes.  The fill-in method is particularly useful when their are potential secondary structure issues.

Hey guys, thank you very much. It works!.

Regards.