If i remember, the secret tech pact lets you get a great sage for 25 gold.
Gambling ring reduces the hammer cost of gambling houses.
Smuggling ring allows you to build smuggling houses in coastal cities, increasing gold (i think it was +25%).
Slave trade i dont remember too well, i think maybe lets you buy 2 slaves.
Then I remember Enlist the Nightwatch, letting you buy one.
Outlaw mana types only affect council members, so it wont stop other civs from having and using them.
Single Currency I believe icreases the number of trade routes between members.
My memory is hazy, havent had a chance to play much in awhile, but hope it helps somewhat.