I used to like a few songs by Norther when I was in high school and I liked a lot of songs by Children Of Bodom when I was in high school but I grew out of both those bands by the time I was 16. oh yeah, when I was in high school listening to these bands I also listened to this band called Mors Principium Est especially the cd The Unborn. They are Finnish as well and have the best keyboardist in any metal band, even better than the guy in Dark Tranquillity.. I've noticed they're pretty popular among Kalmah fans.
I third/fourth the recommendation for Eternal Tears Of Sorrow. the most Kalmah-like albums actually feature the ex-keyboardist of Kalmah and one of the ETOS albums has Kalmah's lead guitarist on lead guitars AND the keyboardist so it sounds very much like Kalmah (A Virgin And A Whore).
http://www.youtube.com/watch?v=GuQ3ayt6c-U - Inferi - Cabal Of Thieves (and all other songs)
http://www.youtube.com/watch?v=4rQ4YG-YdkQ - Synestesia - Talvimyrkky - Two songs from a 2002 demo (Finnish melodic death metal band - all lyrics sung in Finnish)
http://www.youtube.com/watch?v=qPVU1UwURlY - Synestesia - Two songs from a 2003 demo
http://www.youtube.com/watch?v=kjRw9FX5Qo4 - Serpent - Cradle Of Insanity album
http://www.youtube.com/watch?v=QIZkky1BqoI - Shadow - Arrival At The Last Quarter & Towards Obsession (url is to full self-titled album)
http://www.youtube.com/watch?v=EdOgHGuAvE0 - Catamenia - Pimeä Yö (Timo used to be in this band)
http://youtu.be/LpXdFv-OVZc - Holymarsh (korean melodic death metal band)
http://youtu.be/uIsRYSlI8lw - Seducer's Embrace - As The Forest Weeps (Russian melodic death metal band, try to get over their stupid name. their 2002 cd Sinnocence is good)
http://youtu.be/Vy0U03eb-pw - Lunarsea - And The Gardens of Jades Remained Void
http://youtu.be/i2n8w7k7iyU - A Canorous Quintet - Reflections Of The Mirror
http://youtu.be/0pOlVu4PxAk - Dimension Zero - Dead Silent Shriek
http://youtu.be/I8uEMaZvX7s - In Thy Dreams - A Man Of Dreams
http://youtu.be/3VGFweDqNC0 - Eternal Lies - By The Hands of the Architect
http://youtu.be/GD5Hzs1aNLA - Suidakra - Darkane Times
at least do yourself the favor to listen to the first two I listed. I didn't make all the links video because it made this page take forever to load.