My ideal trip would be to fly into Marseille or Barcelona from DC and then on to Palma, Ibiza, back to either of the two I flew into and drive to the other...fly out back to DC. Is this a trip possible in 9-10 days? And if so...any suggestions?
Sure it's possible, but here's how you'd want to do it: Fly from DC into Barcelona and spend a few nights, fly Barcelona to Ibiza (or Palma) and spend a few nights, fly Ibiza (or Palma) to Madrid and spend a few nights, and fly from Madrid back to DC. Not sure where a car comes into the equation, unless you want to drive on Mallorca. In a short trip like this, it's very important to maximize your time by not backtracking; you don't have time to get from Madrid back to Barcelona, and it's not necessary anyway. Furthermore, if you did want to get between Madrid and Barcelona, the train is more than twice as fast as a car.
To find the flights I described in the last paragraph, use the "multi city" option on Kayak, Matrix ITA, etc. Don't look for two one-way flights, as that's MUCH more expensive.
Is it a desirable trip? That depends on the time of year, and what you planned to do in each place. If you post those details, others can weigh in.
Edit: OOPS. I see that you wrote Marseille, but I misread it as Madrid. Sorry.
From Marseille, if your intention is to stop and visit that city, the cheaper flights that I see on www.skyscanner.com all have a connection in Barcelona. Barcelona and Valencia have ferry connections, but I don't see any ferries from Marseille to Spain; see www.aferry.com. Train from Marseille to Barcelona is relatively expensive and takes 4.5 - 6.5 hours. If picking up a car in one country, there's a hefty fee to drop in another.