Small towns along the Lysos River offer the easiest pickings, although of course there's less to loot. Running downriver as far as I've gone, they're named Chorn, Blinth, Oblen, and Altosh. I've heard that the Pharaoh, damn him, will sometimes billet troops in one of these towns, so you could be in for a nasty surprise.
The typical town is square in shape and surrounded by earthwork berms about two metres high. There's a single opening which is barred at night, but any horse except those from the Silkmane clan's herds can easily jump it. You could just as easily ride over the berm. When you enter the town uninvited, be prepared to be attacked by ghosts, which Dinalish Mighty Leap suspects are those of people buried in the earthworks.
Military defenses can vary. Every town has a militia, some of whom are on watch at any time. Their slingers use Oralant's Thunder, which can stun a man and leave him helpless. A Spellguard will sometimes prevent this. Most of the militia fights with swords, although they occasionally use spears. They tend to have little grasp of tactics, but can sometimes overwhelm a raiding party with numbers.
The town itself is laid out in the haphazard style preferred by the vendref, with maybe a hundred buildings. If possible, learn the streets ahead of time or you'll get lost in the heat of the raid. The towns I've named all have open squares which are filled with stalls on market day. The largest building is where the headwoman lives, and will probably have the best plunder. There is always a temple to the vendref goddess Ernalda, which can also have good plunder, but the Feathered Horse Queen has asked we not desecrate earth temples. There are often shrines to Ernalda's husbands, either Oralant or Yelmalio.
Unfortunately, you can't expect to return with many horses, since these people don't have many, and don't know how to take care of them. You can find plenty of cows or sheep to slaughter. The people wear gold, silver, or seashell jewelry, and you can find coins. If you're lucky, you can find wine in portable containers, or else you'll have to drink it out of the barrel. They have much fine dyed cloth and embroidery, and down-stuffed bedding. Many of the kitchens contain large quantities of spice. There are bottles and sculptures made of glass, and furs, and ivory carvings. Some of their weapons and armor is of fine craftsmanship. And of course you can take the people themselves, though this can be more trouble than it's worth.
You can raid most of the farmsteads outside the towns without breaking a sweat, but this will often alert their neighbors, and there's seldom enough to bother with.
I don't know a whole lot about New Crystal City, but Taradarin Ten Day Run led a raid there, and came back with a poppywood runestaff he ransomed back for fifty red horses with golden bridles.
Since they're only vendref, you don't need to worry about pursuit, but they do use signal fires to warn the garrison at Arkat's Hold. Try to avoid them, since they've been known to capture fully laden pack horses with Hobble spells.