man, you're right. most of opeth's song titles are pretty cool, hard to pick the best. i'ld vote for:
serenity painted death
blackwater park
ghost of perdition
as to why ... well, spd and bwp are so cool bc of there inherent paradox. death and serenity are normally not associated. also, a park should rather sport a nice blue pond with fresh water ... no murky pool of mud. yet, you can perfectly picture them both ... the mouth of a skull can easily be imagined to be smiling, thus you have your serenity in death. also, you can easily think of a park that has been abandoned, polluted, intoxicated. it brings up associations, it forces you to see things differently. that's why they are so cool.