Puppeteer
Emperor
February 2007 Update: I've learned that most people don't read the long stuff I type, so here's a quick summary of the two downloads discussed here (with links to their CivFan download page):
Smiley Mood Badges For Your Citizens - Make it easier to see who is happy, who is sad and who is resisting! Never again have a smiling content person fool you into disorder!

Nationality Civ Color Flags For Your Citizens - Easily find foreign citizens in your cities. Great for warmongers needing to know how many and where their foreigners are. (Also has mood smilies.)

Unlike other smiley and flag mods I've seen, each mod includes files for all versions of Civ3 including the shipped PTW scenarios and C3C conquests (like DyP and Mesoamerica).
(end of Feb 2007 summary update)
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This isn't the first smiley popHeads mod by a longshot, but hopefully it's the most complete.
This mod includes epic smiley popHeads for vanilla Civ3 and Civ3 Conquests. (PTW uses whatever vanilla Civ3 is using.) It also has modified smiley popHeads for these PTW Scenarios installed with PTW: Ancient Mediterranean, Balancer and Double Your Pleasure. Now how much would you pay? Don't answer yet, because you also get mods for the Conquests in Conquests! (Oddly enough that's not a repeat.) 11 of the 13 Conquests have their own popHeads files, but upon further review some are copies so there are four unique popHeads in Conquests aside from the epic game.
Some of the Conquests use identical popHeads files, and not all Scenarios and Conquests have special popHeads, so there are only 9 different popHeads files to modify.
Puppeteer's Smiley popHeads (9 popHeads files in 1.4 MB Zip)
Puppeteer's Smiley popHeads with Civ Color Flags (9 popHeads files in 1.5 MB Zip)
EDIT: Editing just to add the phrase "smiley mood badges" and "moodbadges" for the search feature. For more search engine fodder, these mood badges help differentiate happy, content, sad and resisting citizens (or "city workers") as well as providing nationality flags.
Smiley Mood Badges For Your Citizens - Make it easier to see who is happy, who is sad and who is resisting! Never again have a smiling content person fool you into disorder!

Nationality Civ Color Flags For Your Citizens - Easily find foreign citizens in your cities. Great for warmongers needing to know how many and where their foreigners are. (Also has mood smilies.)

Unlike other smiley and flag mods I've seen, each mod includes files for all versions of Civ3 including the shipped PTW scenarios and C3C conquests (like DyP and Mesoamerica).
(end of Feb 2007 summary update)
---------------
This isn't the first smiley popHeads mod by a longshot, but hopefully it's the most complete.
This mod includes epic smiley popHeads for vanilla Civ3 and Civ3 Conquests. (PTW uses whatever vanilla Civ3 is using.) It also has modified smiley popHeads for these PTW Scenarios installed with PTW: Ancient Mediterranean, Balancer and Double Your Pleasure. Now how much would you pay? Don't answer yet, because you also get mods for the Conquests in Conquests! (Oddly enough that's not a repeat.) 11 of the 13 Conquests have their own popHeads files, but upon further review some are copies so there are four unique popHeads in Conquests aside from the epic game.
Some of the Conquests use identical popHeads files, and not all Scenarios and Conquests have special popHeads, so there are only 9 different popHeads files to modify.
Puppeteer's Smiley popHeads (9 popHeads files in 1.4 MB Zip)
Puppeteer's Smiley popHeads with Civ Color Flags (9 popHeads files in 1.5 MB Zip)
EDIT: Editing just to add the phrase "smiley mood badges" and "moodbadges" for the search feature. For more search engine fodder, these mood badges help differentiate happy, content, sad and resisting citizens (or "city workers") as well as providing nationality flags.