I'd also go with digg and stumbleupon. I also like mixx.com. They have a nice atmosphere but they're much smaller so little ito traffic.
I have used digg and stumble but not propeller. The first two definitely help you in boosting traffic. Third one I have to test and tell
Digg, Propeller & Stumbleupon can all generate a lot of traffic but you have to be sure to become part of the community and make friends, after that you need to use the tools that they all offer to follow your friends and vote their submissions up and comment on their submissions. They all also have great tools that allow you to send your submissions to your friends so that they are sure to see them and will likely give you votes and comments as well. I have found that this is how most of the top users use these sites to get traffic and you will not do too well if you just go there and submit your articles and leave.
I love netscape. After its recent change to propeller...it is considered to be one of the top social bookmarking sites.