In international, you can visit Switzerland, France and other European countries as climate will be pleasant
in India, you can visit North India , leh Kashmir, Jaipur, ajmer .. nad a pleothora of places
It depends a lot where will you be traveling from and kind of place like mountains, plains or beach. Although you will find Gushaini (and few other places in Himachal Pradesh & Uttarakhand), Darjeeling and Sikkim really pleasant at that time. If It's early May try tiger sighseeing at Ranthambhore or Bandhavgarh.
I was in kashmir, ladakh and manali in may last year. Did a backpacking trip for 3 weeks, and iam so glad that i choose that time of the year. it was all just so lovely and perfect.