I just got back from a fantastic two week trip to Argentina and Uruguay. Here's an idea of my itinerary, which I hope some might find helpful...

Buenos Aires - Stayed at Hotel Vitrum in Palermo Hollywood. Upscale, artsy and excellent service. Highly recommend it. Took a bike tour to Tigre with Urban Biking and then booked another to the northern part of Buenos Aires. Super friendly guys, took us to places most tourists probably don't get to visit. Saw a great tango show in San Telmo (btw, I like San Telmo a lot more than La Boca). Had some great meals in the Las Cañitas area. Thought Puerto Madero was nice but overrated.

Uruguay - Took the Buquebus to Colonia, where I spent one day. Quaint, peaceful little city. Headed to Montevideo for two days, stayed at the Sheraton. Had a great lunch at Mercado del Puerto - definitely try the meat and have a bottle of Medio y Medio. Rented a car and headed to Punta del Este - gorgeous beaches, beautiful people, great food. Went up to La Paloma and La Pedrera - nice little beach towns with great waves for surfers. Cabo Polonio impressed me most of all - rolling sand dunes, fishing village vibe, very rustic.

http://www.vitrumhotel.com/
http://www.urbanbiking.com/
http://www.mercadodelpuerto.com.uy/
http://www.buquebus.com/
http://www.starwoodhotels.com/sheraton/property/overview/index.html?propertyID=1238