http://www.naturalreaders.com/
Free Natural Reader 7 is, well, free.
It will give you the necessary tools for text-to-speech usage.
http://www.readplease.com/
This isn't free but I think you have a trial or you can download the free version. Not sure.
http://www.text-to-speech-software.com/
This isn't free either. It only has trial version. It has a simple UI.
http://www.spacejock.com/yRead.html
This is free. This is for XP and Vista users.
http://www.nextup.com/TextAloud/
Not free. Free trial only. Requires very little things for it to work properly.