I gotta post my .02, hopefully it's worth more than 2 cents. Because I've been experimenting with Sedo, Namedrive, DomainSpa, and DomainSponsor.
I've had my names at Sedo, they are good for selling domains and the parking is ok. Kinda partial to them, since that's the first place I ever used and it was a good experience. However, I don't like the landing pages - very generic. And they will not let you park names that have trademark possibilities (such as googleearthwebpage.com, just made that name up).
DomainSpa filters foreign traffic - I won't use them again. They were the second (2nd) PPC I used, I then put my names back with Sedo.
Last month I found out about NameDrive and thought I'd give them a try. I really like these guys and what they are doing. They've helped consult on 2 domain sales without a charge. Great landing pages and great stats with breakdowns of region and search topics. But, I've noticed a PPC$ similar to Sedo's and it's not high. Even though they have a low PPC$ - sometimes all those other things outweigh the $ when parking the names, especially if you plan to develop the names anyways. High traffic names do well.
I just tried DomainSponsor. Been using them for 3 days now. My traffic has gone down substantially from what it was at NameDrive. And so has my revenue. I've read that 'redirect' services don't capture all the traffic - don't know if that's true or not, but I'm thinking that it is because of what I've experienced at DS. My Click Thru Rate was higher at NameDrive also. I know alot of folks have said that DomainSponsor does really well, but I haven't noticed anything better than the rest of the average PPC's.
But, for now I think I'm going go back and stay with NameDrive. I don't like having to manage more than 1 PPC provider because that's just too much domain managing. Staying with 1 is best for me. In the meantime, I may check out Skenzo.com - someone mentioned them to me earlier today.