Anything by Bikke.
in my closet, cute story, funny and hella cute
It's not really underrated but 'Never Understand'
http://www.mangago.me/read-manga/umibe_no_etranger/ Theres a second volume once youre done reading the first. Its super fluffy and light hearted. Has a yaoi tag but its not that intense.
My shounen ai list. Some great ones here. http://www.mangago.me/read-manga/kokoro_kanda_neko/
^^--Ignore. This is the real list, sorry. http://www.mangago.me/home/mangalist/276082/
any underrated shounen-ai stories? basically anything you think is definitely worth reading lol