How in the heck do you manage that? When I'm playing huge maps even with 100% morale I can rarely keep the tax rate over 35% without people getting pissed.
End of quote
Well, first I never take the "Speed Boost" advantage that so many players here live on. Starting the game with 3 times more planets than your closest opponent makes the game boring for me. I prefer big epic zillion turn galaxy conquering huge maps with wars that last decades and involve conquering a dozen planets (still leaving the enemy with a sizeable viable empire). Maps big enough that there are actually individual "sectors". It gets almost like playing 3 or 4 games simultaneously.
By avoiding the heinous cost of the Speed boost I can afford to take Morale boosting and occassionally the morale boosting government too.
I don't know what the morale algorithms are but in my experience it seems to be that once a people are pissed off they are likely to continue to be pissed off. Therefor doing things that piss people off in the short term seem to make manageing morale in the future that much harder. Conversely making people happy with artificially low taxes simply builds in them the expectation of low taxes making raising them difficult. By starting off with high taxes right from the beginning, the game seems to accept that as a "normal" level.
But the REAL key to high morale regardless of anything else is the economy. Morale resource bases are a good sledgehammer approach, but on a big map the single most important resource is Econ. Build every econ building you can. Trade, alot. Some people like to build a trade starbase in every sector along a freighters route. I find its MUCH easier to make sure all of your routes originate from the same sector, travel as short a distance as possible (a nearby minor is ideal) and then concentrate all of your Trade modules in that origin sector...piggybacking on the production and Mining starbases you'll have already built there.
Why a high econ...because then you can build ALL of the morale enhancing social projects, including things like medical centers and embassies and such.
Also key to this strategy is making sure you have 1 starbase with maxed out production enhancers in EVERY sector having at least 2 planets (and all if you can afford it). The production boost is necessary because building alot of social projects (all of the econ and all of the morale) requires alot of building. By maxing out production boosters you can build everything quickly and still keep Social Spending modest relative to Research and Military.
Morale trade goods are also helpful. Managing population is another important facet. Build alot of combat transports and load up 5 billion people any time the planetary morale starts to drop below 80. The impact on tax income is marginal, and in a big galaxy you'll have plenty of uses for invasion fleets.
CTs also make excellent defense ships to park on Starbases, so after loading them up, I always muster my forces on a starbase.
So to summarize. My keys to 100 100% happy planets.
1) don't waste points on Speed or Military civilization choices. Buy Production, Econ, and Morale boosting options and governments.
2) Use Econ resources, Trade, Trade Starbases, and econ boosting buildings to generate beau coup money (I'm NEVER short of cash past the early game).
3) Use Production starbases and Production Boosting buildings to give you a huge edge to building social projects so you can keep your spending in Military and Research up.
4) Keep building morale increasing buildings on your planets starting with PQ improvements (or sometimes the Entertainment Center is better for planetary growth to buy after Soil and before Habitat). Stadiums and Teleporters and Stock Markets on every planet. Multimedia and the lesser 5% boosters as needed.
5) Build ALOT of Combat Transports and use them to keep your population at decent levels. I generally avoid just "spacing" people...I consider this to be a draft where soldiers are held in stassis aboard troop carriers until needed.
The REALLY great thing about this is that its a synergistic circle. Morale has a HUGE impact on tax revenue. 100% gives you more money, which you can then use to keep 100% morale...which gives you more money.
During the game where I went for Tech victory, it took so long to get there that I had virtually every building on every planet, heinous amounts of maintainence and was still rolling in more cash than I knew what to do with...and that was without selling tech for cash.