I agree that it would be nice if there were a tooltip that would come up with the effects and expiration date/turns remaining anywhere that you can find the treaty listed.
For your information, and for that of others, until such time as a tooltip gets added:
Trade Treaties increase the income of the signatory factions by 10%, and last until cancelled (or possibly until one party is destroyed, but I've never bothered checking).
Economic Treaties create a trade route between the capitals of the signatory factions, providing a 10% income bonus in that city. This treaty also lasts until cancelled, and I also don't really know what happens when one of the capitals changes hands or when one party to the treaty is destroyed.
Tribute Treaties take 10% of the income of the paying faction and grants it to the receiving faction. This treaty lasts for 30 turns and also enforces peace between the signatories for that period. As far as I know, this treaty cannot be cancelled.
Non-Aggression Pacts last for 50 turns and prevent the signatories from declaring war on one another in that time. I don't believe you can cancel these treaties.
Alliances require that the allied nations declare war on any nation which issues a declaration of war against one of the signatories, but don't contain any requirements about supporting an ally in a war that the ally started. I believe that if two of your allies go to war with one another, one of the alliances gets cancelled, since you're required to go to war with the aggressor. Other than that, I don't believe that there is a way to get out of an alliance early. Alliance treaties last for 99 turns.
Surrender treaties are permanent and irreversible, and result in the sovereign of the surrendering faction joining the faction to which they surrendered, acting as a champion of that faction. If the surrendering sovereign had an ability that provided a faction-wide bonus, the bonus is granted to his/her new faction. All other remaining settlements, outposts, units, and structures disappeared from the map the last time I was able to get an AI to surrender; I don't know if they've changed this or not. If you offer your surrender and the AI faction you offered it to accepts, you have lost the game.
Research Treaties provide a 10% bonus to each signatory faction's research production, and last until cancelled.
Peace Treaties end hostilities between the signatory factions. As far as I know, you cannot make alliances in such a way that you cannot make a separate peace. Also, there doesn't seem to be any restriction preventing you from turning around and declaring war again immediately after signing a Peace Treaty, although I think that results in a diplomatic penalty with all other factions in the game.
