My sister and I have two nights to spend in Barcelona on both ends of our cruise in May. I'm looking to make reservations at two moderately priced places to eat -- one that is an "old world" establishment, and another that is a trendy modern spot. Suggestions?

Not sure what "moderately-priced" means to you. I had an excellent meal at Comerç 24, which would fit the bill for "trendy". The chef, Carles Abellan, worked under Ferran Adrià of El Bulli for years before opening his own restaurant.
www.comerc24.com

If it's too pricey for you, you can always try its cheaper sister restaurant, Tapaç 24.

I second the Comerc24. It is an outstanding dining experience, much different from traditional dining.

I would go there, even it may be a little above "moderately priced". You may compensate this extra-spending by eating the other time in a low-cost restaurant like Mercato Santa Caterina (modern, hip but reasonable priced traditional dishes like suckling pig or paella) (http://www.bcnrestaurants.com/Eng/ba...santa-caterina)
or Nou Celler, Carrer de la Princesa (very traditional, rustic atmosphere).

For the modern restaurant, Cinc Sentits.

http://www.cincsentits.com/

For Old World you could try Los Caracoles.

Don't know if this qualifies as "old world", but Cal Pep is incredible, and for "trendy, modern," The Attic comes to mind. I don't believe Cal Pep takes reservations for less than 6, but it was worth the wait, and The Attic may takes reservations.

Cal Pep and Cinc Sentits.

Cal Pep could almost be both - the place is outstanding and has character to spare(including the chef!!) but it also has wonderful forward thinking food that uses the best fresh ingredients of the day in neat and unusual ways. They don't take reservations so you just need to line up at the door when you get there. I think a small dining room has been added so its not just the 12 or so stools as before...but the granite counter really impressed!!!

Thanks for the advice! Can anyone give me an idea of the price range at Comerc 24 - like whether the meal for two would be well above $100? The menu posted online lacks prices.

jessvs-

$100 for two doesn't go very far these days. With the $ being so weak, it'll come out to just €63.

Comerç 24 is definitely a lot more than that. I cannot remember what the a la carte prices are but they're not cheap. I went for the cheaper tasting menu (they offer 2), and it was €62pp (not including drinks/tips).

Oh, I also had dinner at Attic Restaurant. It also is modern, but much easier on the wallet.
http://www.attic.angrup.com/english/index.htm

I had an appetizer plus an entree (and a bottle of water). That was just €22.

I suggest you the follwong website, where you will find a good list of all kind of restaurant in Barcelona.
http://www.thefork.com/1_restaurant/...restaurant/23/
You may also book directly your restaurant for free.