I agree with flights that involve multiple places. But there are also lots of RTW trip options. I've done a RTW trip myself with 5 destinations, and even then the options were a bit mind-boggling.
It was my first RTW trip so I spent a few hours looking up different RTW tickets, as well as figuring out what destinations to go to, how many stops were available, etc.. I ended up researching online, and then going to see a travel agent twice. I even brought an atlas with me the second time to see the agent! I also spoke to a couple of friends that have done RTW trips to get their perspective. Then you have to consider frequent flyer miles and what destinations, seasonality etc...