Age of Empires - Tool Age upgrades

The only upgrade that the Stone Age offers is the upgrade to the Tool Age (costs 500 ) - Stone Age people were too dumb for research ;-)

This page does not only list up all upgrades, but also explain their uses and advantages.
Barracks - Storage Pit - Granary - Market - 2nd part (Bronze Age)

Barracks

Upgrade to Axemen +2 attack, +10 HP cost: 100

Description: While Clubmen are not more than souped up villagers (having more hitpoints, but otherwise no improvements), Axemen are the top reason why you should quickly upgrade to the Tool Age. An Axeman can kill two Clubmen 1 on 1! However, Axemen cannot be upgraded later so you have to think twice before investing a lot of food in them.

Storage pit

Toolworking +2 melee attack 100	Leather Armor +2 Infantry armor 75	Leather Armor +2 Archer armor 100	Leather Armor +2 Cavalry armor 125

Description: The first upgrade you should get is the Infantry Armor: it makes your troops a lot stronger. It is cheaper and better than the weapon upgrade! (For details look at the combat equation section).
Leather Armor for Archers is also very important if you want them to survive. Archers have no armor before they are upgraded, making them an easy prey for Axemen.
The weapon upgrade is also a great improvement for your Axemen, if you have more than four of them, get it!
Only the Cavalry armor is useless in that stage. You should not use your weak scouts for fighting, and you have no Cavalry yet. You can wait until you have started the upgrade to the Bronze Age with this one.

Granary

Small Wall 200 HP 50	Watch Tower 100 HP 50

Description: Since towers and walls cost stones, you are very restricted in that part of the game as long as you have no villagers mining stone.
A Watch Tower greatly improves your defense since Axemen have no armor against arrows. It is very hard for Axemen to kill a Watch Tower and nearly impossible if you have some Axemen yourself. A good idea is to protect your villagers at the Granary and the Storage pit with a Watch Tower.
A wall is, unlike in Warcraft, a powerful defense. If possible, wall off some sections of your village so you can easily defend it with some Archers. Towers are a great defense against Archers and Axemen, so get them up fast!

Market

Woodworking +1 missile range +2 woodcutting	Stone Mining +3 Stone Mining	Gold Mining +3 Gold Mining	Domestication +75 farm production
120 75	100 50	120 100	200 75

Description: The Market is the most important building of the Tool Age because it lets you get farms, without which you will soon run out of food unless you live near a lake with much fish. You should get these upgrades after the weapon upgrades if a war is imminent (i. e. on land maps).
Woodworking is definitely the best of one of these upgrades. It increases the amount of wood that your villagers can carry which is important because the villagers will have to walk an increasingly long way from the Storage Pit to the trees. The increased missile weapon range can be helpful if you have walled in your city.
The upgrades for Stone Mining and Gold Mining are not that useless after all. They do not only increase the amount of Stone or Gold that your villagers can carry around, but also the speed at which the resources are mined. Upgraded villagers will mine 30 % faster. So the Gold Mining upgrade is certainly an important one since gold will be crucial after the Tool Age.
Domestication increases the amount of food that is produced for new farms, but not for the farms you already have. So get this upgrade before building farms! Usually I get some farms going until I can gather enough food for this upgrade. Then I build more farms. Note that the upgrade will not increase the speed at which food is harvested. You will have to rebuild farms less often with this upgrade, so it will affect your wood resources rather than the food resources. This upgrade will also help you if you get caught up in combat and have no time to rebuild all farms.

Special thanks go to Mr. Grinch for his great tips.