Another way: Set up bottlenecks and blow up crowds in the bottle. This takes a good few MP to execute, but it's lots of fun.
Get in a corridor or other spot where you can block the entry. Drop Conjure Flame in front of you so mobs will not advance.
Cast Inner Flame on a mob on the other side of your flame cloud. (Pick a weaker one you can kill fast.)
Allow multiple mobs to group around the one with Inner Flame, as much as timing allows.
Kill the one you have Inner Flame on, and watch the others burn.
Be aware a few mobs (yaks! hydrae, some uniques...) will march right into a flame cloud. Don't cast Inner Flame on those unless you have serious Fire Resistance!
I have no idea what the standard ASCII symbols are. I just made this up:
. = ignore these (I couldn't just use spaces)
ccccc = corridor tiles
Y = You (standing in corridor)
% = your flame cloud (from Conjure Flame, blocking corridor or doorway so mobs can't reach you without entering fire)
w = walls of room (where more mobs can gather while waiting to go forward)
T = targeted this mob with inner flame (for example, or you could have targeted either of the two others now standing next to it)
M = other, adjacent mobs waiting in room - all of these will be engulfed in fire if you can destroy T while Inner Flame is applied
............wwwwww
............w
............wMM
cccccccYc%TM
............wMM
............w
............wwwwww
Note: Not sure if the spacing is clear enough, but you want the crowd of mobs just inside the room and your flame cloud in the doorway (more precisely, in that wall of the room). That way, you can pick from any of the three leading mobs for Inner Flame.