Travel Guides and Advice

A couple of initial pointers

1.) Renting a car in one country and dropping it off in another does incur in very heavy extra costs. Just for your to know in case you were planning to do so. If that's the case, I strongly advice to rent a car in Barcelona, do your sightseeing in Catalonia and drop it off in Port Bou (just by the border with France), take then a short train ride to the other side and rent a new car in France. In all you'll save a bundle.

2.) For your leg of the journey in Catalonia, I advice to start planning by looking at these helpful websites:

www.catalunya.com
www.infocatalonia.eu

The first one is Catalonia's Tourism Portal and contains plenty of information including downloadable free brochures, guides and maps. Then, if you're particularly interested in any specific region of Catalonia, each one has its own "tourism portal" with more detail about the area (ie. http://en.costabrava.org/ for Costa Brava, etc). You can just browse it in Google, or ask me and I'll provide the appropriate link. The second one is a video portal so you get a feeling of what an area is like before even having set foot there as well as other useful information (ie. events, festivals, traditional and folk activities, etc)

To get your bearings about the names of the "vegueries" (sort of your 'states') in Catalonia, check this: http://www.infocatalonia.eu/w/map-of-catalonia/ and then for further refinement check the map of "comarques" (sort of your 'counties'): http://bit.ly/CATcounties

As the previous reply states, it's costly to drop a car off in a different country. We did a similar trip in reverse, but we drove around the southern part of France and then turned the car in and took the train into Barcelona, which worked great and saved money.
We stopped in Figueres for the Dali Teatre-Museu as it's north of Barcelona on the train line and easy to access without a car.
Happy travels!

Thanks for your helpful advice. I should have added that we're planning to make a "circle", Spain-France-Spain.

I look forward to more interesting tips

How long do you have for this trip? What are your interests (and conversely, what specifically does not interest you)? Have you been to any places in the area before?

The more information you give, the better answers you will get.

Also to clarify, the Loire Valley is approx 550km from Geneva.
As previously mentioned cross border car rental is expensive.
You may find it way cheaper to pick up a car in Montpellier for a rental entirely within France.
Drop off (depending on how you finalise) in Annecy, Lyon, Orleans or Tours.

If you drive in Switzerland, you will likely need a vignette for your rental car. You don't want to get a fine for traveling on the highways that require it without one.

Also, you will need to get money in Swiss Francs, requiring that you add Switzerland to the countries your credit and debit card providers need to know about. Unless you have a burning reason to go there or are going to spend some quality time there or are unwilling to leave you car in France and take a train or bus to Geneva, I wouldn't bother.

Heed the advice about the distances in France. Rome2rio can help with that. For example, Barcelona to the Loire Valley (Tours) would be a very long drive. If you look at the map, Barcelona, Tours and Geneva make a big old triangle.

When you use Rome2rio, make sure that you are getting your info in EUR and Kilometres. You can set those options on the far upper right of the page where there's a currency indication and a little round gear.

Assuming you haven't driven in Europe before, I recommend that you thoroughly explore Gemut.com, especially the brochure What You Should Know about Renting a Car in Europe. Andy can also help you with car rental and advice.

When comparing Rick Steves' guidebooks, note that the France book and the Provence and French Riviera book do not fully overlap; the smaller book covers some destinations that are not in the bigger book.