Widow Remarriage

it has been stated in valmiki ramayana by valmiki himself that after the death of vali,sugriva married his widow tara 
http://en.wikipedia.org/wiki/Tara_(Ramayana)#Marriage_to_Sugriva
 
After the death of Ravana, Rama advises Vibhishana to take Mandodari as his wife, even though he already had a wife. A theory suggests that to restore order in the kingdom after Ravana's death, it was necessary for Vibhishana to marry the reigning queen to get the right to rule. The marriage between Mandodari and Vibhishana is seen purely an act of statesmanship. Another reason for the marriage could be that it was an alternative to suicide for the widowed Mandodari, which is averted by Rama.
http://en.wikipedia.org/wiki/Mandodari#Marriage_and_later_life