I just completed my first trip to Buenos Aires. I found Ana by sheer good luck, and I can't say enough about her punctual and courteous professionalism. And to boot, her translation service was outstanding considering that my Spanish is zero.
Ana is an Argentina, and has lived in Naples, so she understands cultures of both countries.
She offers myriad of services with very reasonable fees for the tourists, including airport to hotel/city transportation, private city tour, estancia tour, and other services.
Compared to other remis or other tour services, since she operates her own vehicle, her prices are extremely reasonable. For example, she only charges 50 Pesos (that's less than $18 USD at current exchange rate) for airport transportation.
I would highly recommend Ana to anyone planning a trip to Argentina (especially if Buenos Aires is primary venue).
Her website is: http://www.ana-luna.com