Does anyone know if there is a rental car company within walking distance of the train station in Tarragona? Not the camp de Tarragona! but the actual one that is in the city?

That's one for Google, and it shows Hertz as the closest.

There is a Europcar rental office at Hotel SB Express, Plaza de Les Corts Catalanes, which is a short walk from the station.

Hertz = 250 ft from station
Europcar = 2.8 km (1.7 miles) from station

There are a lot of car hire offices. Here is a map of them:
http://bit.ly/tarragonamap

The Hertz office michelhuebeli posted about is the only one I would want to walk to if I was carrying any luggage. Not only is there the distance, there is also a rather large hill to contend with.

Do make sure to book directly with Hertz in this case. On another of your threads I wrote about an Autoeurope reservation in September where the "Tarragona downtown office" ended up being in another city entirely. Next time, I will rent directly with this Hertz office.

Kemwel offers the Hertz location across from the rail station in Tarragona, Carrer Del Comerc 3, at a slight discount over what Hertz is charging, but not big enough to make a difference unless renting a standard size car. If you are a Hertz Gold Plus Rewards Points member, you could earn some more points.