Arunachal Pradesh, Assam, Meghalaya, Sikkim

Arunachal
http://india-tourism.com/en_apr.0.html

Meghalaya
http://eastindiavyapaar.com/travel/meghalaya/meg_tvl_shil.htm
HOW TO REACH

Guwahati is the gateway to the North East including Meghalaya. Best way to reach is to fly in Guwahati, which is well connected, by air and train from Delhi and Calcutta. There are daily flights to Guwahati as well as train service from Delhi and Calcutta. Jungle Travels staff will receive you on arrival and arrange transfer to your destination.

http://india-tourism.com/en_meg.0.html
Any time of the year is the right time to visit Meghalaya. Often likened to Scotland for its topography, scenic beauty and vegetation, it presents a panorama of lush, rolling hills; heather-covered slopes; breathtakingly beautiful waterfalls; mountain springs; moving mists; silent lakes, and a multitude of flora and fauna, including rare and unique species.
All its charms are made doubly attractive by its climate; on the whole cool and temperate right round the year. Even the coldest winter has a touch of spring, and even the monsoon months are a Chlaroscuro of dark, rain-laden clouds and bright sunshine. Its climate makes Meghalaya that rare hill-resort country that is a pleasure to visit round the year, even at the dead of winter.
http://www.tourismofindia.com/sts/stmegplaces.htm


Assam
http://india-tourism.com/en_ass.0.html

Sikkim
http://india-tourism.com/en_sik.0.html