I agree with this article, open source products are becoming more inviting due to the cost differences - this also being true for iSCSI targets.

Although I'm sure each of these iSCSI targets have their strong points and weaknesses, I would say that the best option is actually the SUN OpenSolaris COMSTAR iSCSI target. From this list, I have only used IET - which works well with the Microsoft iSCSI Software Initiator. However, I had some issues using it VMware ESX 3.5 and 4.0.