If you seige a city and it sallies you will get the income from that city on the turn you just ended. Some cities will only sally if you don't have a general in the unit and others sally with just a few units.

Here are a few of my favorite sally cities:

1. Dublin will sally with General Bodyguard, Mailed Knight (optional) and Peasant Archers. Easy Heroic Victory.

2. Bordeaux will sally with Mailed Knight and Peasant Archer. Easy Heroic Victory.

3. Rennes will sally with the stack that England start with that is closest to it with Mailed Knights added to the stack to have a chance of winning.

4. Alleppo and Adana will sally with a GBG and a Heavy Cavalry or Hore Archer. Challenging but do-able.

Anyone know of some others?