I would just like to reinforce some things already said, and add a couple:
(a) It is important to get your names in front of eyes, so do list at as many marketplaces as you feel comfortable with.
(b) Do look at the commissions and other requirements though, and you may decide some venues are not good for certain names (i.e. if the name is anticipated selling for only say $120 make sure you are not paying half or more in fees).
(c) Make sure that you only have it with a Buy it Now price at one location, and all other are Make Offer. Otherwise it is possible it could sell twice simultaneously and you are in business/legal trouble. Odds are low, but still...
(d) In addition to the venues mentioned already, I would recommend Undeveloped. They have great landers, reasonable commissions and are very responsive.
(e) When your name sells, don't forget to take it down everywhere. More often than you would think I find names that are long sold still listed. This is unprofessional and can make someone upset.
(f) After a domain name has been registered or transferred in general it can't be transferred again for 60 days normally. I know some on NPs list them right away, but for me I don't list at the standard marketplaces until the 60 days are up, since if it sold but could not be transferred right away not good. You could list it as offer on say your own Efty, but make it clear it is only available to push at the existing registrar to the new owner. During the 60 day period you can list it on a registrar Marketplace if they have one (e.g. NameSilo and Namecheap do), since a sale there is automatically handled as a push to the new owner's account at the same registrar.
(g) Afternic has a huge premium network, but to be listed there depends on both what extension it is and where it is registered. If you want Afternic premium coverage choose a registrar that supports that. You can find the list on Afternic site.
Good luck with selling your domains!