Prayers have been answered!
Midnight Slayer
In the new fansite Friday Gaile said that anet was working on developing a more sophisticated trade system for the future. This will change a lot of things and hopefully stop all that trade spam.
Shagsbeard
I hope that "sophisticated" translates as "removes entirely the POS trader system we have currently and replace it with something that provides characters a fun reward for any item they find, even those not immediately sought after by the rest of the playerbase."
ShadowWrath
Or at least increase the sell value to NPCs.
boxterduke
yay, my throut is tender from yelling WTS and WTB
Vorlin
Here's a system I've seen used on a Mud I used to play on that might be fairly easy to implement in GW:
1. You have a trader specifically for selling player gear.
2. When a player wants to sell something, they click on this trader, click on the 'Post Item' button. This brings up a screen where you can click on the item in your inventory you want to sell.
3. The game then asks what price you want to ask for the item.
4. After entering the price, the item is removed from your inventory and added to that trader's database of items for sale, along with your price and a tag that identifies you as the seller so that later if it's sold your character gets credited with the money.
5. You click on this trader at any time and see a list of all the items you have for sale, allowing you to cancel a sale and have the item returned to you.
From a buyer's point of view, you click on the trader, ask for a 'Items for Sale' screen. If you see an item you want, you click on that. The screen then displays all items of that type along with the price being asked for them. You buy the cheapest one (if you still want one).
This system pretty much uses the current trader interface (with a few new additions that should be easy to code), it allows many items to be sold of the same type, it allows the seller to set a price, and it allows the seller to reclaim the item whenever they want. Anyone wanting to buy an item can immediately see if anyone in the game is selling it, so no more 'WTB...', and they'll always pay the best price possible.
Probably too late for suggestions of this sort, but it was on my mind so figured I'd post it.
1. You have a trader specifically for selling player gear.
2. When a player wants to sell something, they click on this trader, click on the 'Post Item' button. This brings up a screen where you can click on the item in your inventory you want to sell.
3. The game then asks what price you want to ask for the item.
4. After entering the price, the item is removed from your inventory and added to that trader's database of items for sale, along with your price and a tag that identifies you as the seller so that later if it's sold your character gets credited with the money.
5. You click on this trader at any time and see a list of all the items you have for sale, allowing you to cancel a sale and have the item returned to you.
From a buyer's point of view, you click on the trader, ask for a 'Items for Sale' screen. If you see an item you want, you click on that. The screen then displays all items of that type along with the price being asked for them. You buy the cheapest one (if you still want one).
This system pretty much uses the current trader interface (with a few new additions that should be easy to code), it allows many items to be sold of the same type, it allows the seller to set a price, and it allows the seller to reclaim the item whenever they want. Anyone wanting to buy an item can immediately see if anyone in the game is selling it, so no more 'WTB...', and they'll always pay the best price possible.
Probably too late for suggestions of this sort, but it was on my mind so figured I'd post it.
Aria
There has been no timeline announced, so please keep in mind that it might take a while. In the meantime, there's no reason why you shouldn't keep thinking of good suggestions for a trade system. Just remember to post it in the sanitarium! 
Midnight Slayer
I just hope they add something like an auction house or maybe come up with their own creative idea.