NPCs
Good idea for a topic.
My current campaign has been running for almost 3 years and so has allowed time for good NPC development. We are actually nearing the end of the campaign, and during trials and tribulations some NPCs have died. Like in life, sometimes you don't know how much you like someone til they are gone.
Two NPCs in particular had interesting impacts. One was Thorgrimm, the gifted Smithy who would give the party some information, repair/customize gear, and tell stories to. He was somewhat minor, but did have the important role of bringing the party together in the very beginning when the dwarf called upon various friends (the PCs) to help him in a troubling matter.
Well, in my campaign the Horde (goblinkind, giants, ogres, etc) will frequently try to exterminate other races in massive numbers, and they ransack the outer city where Thorgrimm works and lives, and his Smithy is razed with the rest of that part of the city. Later, Thorgrimm's broken body and the Smithy's store sign turned upside down are carried into the next wave of battle against the city by the Horde. The PCs are part of the defending army and face the elite Lizadrman detatchment carrying Thorgrimm. For many PCs I learned that this was quite motivating and shocking, and they wrought their revenge on that enemy.
The other NPC I will mention is General Cramm. Cramm was the party's main contact into the military of the region, an advisor, and father-figure to one of the PCs. He was made interesting by being gruff but pragmatic, concise but willing to belt out a rusty song, and he was mortal. In fact, one player needed to roll up a new character and we made this an actual son of Cramm, creating an interesting tension/relationship with the PC who viewed Cramm as second father.
Well, Cramm is a general in this war torn area, but before he sees his final battle, he is poisoned. I had planned on killing him here, but thought "what would Cramm do?" He was dying in his bed, but instead of entering the final sleep, he stands and says, "Bring me my sword!"
He rides into battle defending the city, never to return. A fitting burial scene followed the battle, a battle in winning which the PCs were pivotal in of course.
But man I miss Cramm. He was great, but he did his duty and led a great life for an NPC, including frequenting a brothel and dressing up as a minor soldier to engage in battle as an everyman.
One last quick blurb: I took over a PC when one player left, and that now-NPC became very interesting! He changed allegiences and passions, but in ways that followed the traits the player had introduced, creating a great opportunity for PC and NPC interaction.
Long live the three dimensional NPC!