DDO's microtransactions work on an in-game currency called Turbine Points that you buy with real money. Subscription players (called VIPs) receive 500 Turbine Points per month as part of their subscription although this stipend has been subject to some delays since Eberron Unlimited went live.
Turbine Points have a real world cost that varies according to how many you buy at once. It is also occasionally possible to see them offered at discount prices. At their absolute cheapest you can buy 5000 points for $49.99. The standard rate for the smallest points package is 400 points for $6.25.
So the real world value of Turbine Points is between 1 cent and 1.56 cents each.
The current top sellers in the store are:
Major experience elixir (grants 20% bonus to experience for 6 hours) 295 TPs
Siberys spirit cake (returns target to life, 1 use, not usable in raids) 150 TPs
Moderate heal potion X 50 (each heals 5-19 hit points) 150 TPs
Greater experience elixir (grants 20% bonus to experience for 3 hours) 195 TPs
Medium Jewel of Fortune X 5 (each grants +1 level to loot found in chests for 6 hours) 125 points
Drow race (create a Drow character on any server, permanent upgrade) 795 points
Cleric lvl 1 - Dryad Willowisp (level 1 cleric hireling, 1 hour Gold Seal contract. Gold Seal contracts allow the use of multiple hirelings) 10 points
Lesser experience elixir (grants a 10% bonus to experience for 3 hours) 50 points
Moderate heal potion X 10 (restores 5-19 hit points per use) 50 points
Secret Door Divining Rod (reveals secret doors for 5 minutes, 1 charge) 30 points
Barbarian lvl 1 - Byron Scoutsword (level 1 barbarian hireling, 1 hour Gold Seal contract. Gold Seal contracts allow the use of multiple hirelings) 10 points
Shan-To-Kor (level 3-5 adventure series with 4 adventures and 2 combat area objectives)
I've listed the items in the order they display in the Bestsellers section of the DDO store. I believe it's in order, ie the first item on the list is the item they sell most of.
None of these packs are on special offer. The only notable thing missing which is usually on the bestsellers list are the sigils of levelling. However these have been on sale the last few days so possibly there was a rush for these on day 1 of the sale so no one needed to buy them in the time period for which the data for this bestsellers list is collected (I'm guessing it's based on a 24 hour period, collected once daily)
I'll analyse the list tomorrow, I think it's very interesting to see what most people are buying.