Alexis,
I'm not sure I would look at in terms of what within Campy is similar to 105, although I'd say anything Veloce on up is as good as or better than 105. But in saying that, I know that 105 has gotten a lot better over the last few years, so perhaps Centaur is a closer match. Really, though, it may just come down to how much you really want to spend.
I do think you get a fair amount of bang for your buck with Centaur, but I haven't looked closely at Campy's offerings for the last couple years--since I built my last bike with Centaur--to appreciate how it differs from Chorus or Record. I chose Centaur in part because of price and also because it offered an alloy crank, which is what I wanted. In truth, I preferred the hoods of my 2006 Veloce, so while the my 2009 Centaur group is better, I liked the functionality of my older groupset.
For that reason, I would suggest going to your local shops and actually trying the various groups and manufacturers. You may find that your hands simply prefer one or the other. Also, have you factored in changing your wheels/hubs if you switch from Shimano to Campy? If I understand correctly, your Shimano-compatible wheels will generally not work with a Campy drivetrain.
I will say this: a lot of shops just don't like working on Campy anymore. Thankfully, that's not an issue for me because I have my own mechanic, otherwise known as my husband, but when I was relying on shops, I found some degree of resistance. Campy often requires Campy-specific tools, that just aren't cheap. Parts themselves, e.g., cassettes and chains, aren't cheap either, so it can cost a little extra money over the years to run Campy.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher