Not sure about underrated, but a few that may have slipped under the radar for some:
Helmet – Meantime
Quicksand – Slip
Refused – The shape of punk to come
The Young Gods – L’eau rouge
The Wedding Present – Seamonsters
Lucero – That much further west
Life of Agony – Soul searching sun
Cave In – Antenna
Entombed – To ride, shoot straight and speak the truth
The get up kids – Something to write home about
Promise Ring – Very emergency
Leatherface – Mush
Seafood – When do we start fighting
Seaweed – Four
…….could go on forever 🙂