The major telco providers are Claro, Movistar and Personal, which each sell prepaid plans to non-residents. Data is available from Movistar, and it's still listed prominently on their website for the Prepago plan:
10-15 Argentinian pesos. These cards can be used for the following 3G data access.
(in Argentinian pesos)
1 hour $3 2 hrs $5 4 hrs $7 6 hrs $10
1 day $20 2 days $30 5 days $50 10 days $100
to activate send an SMS to: 454 with: 1h, 2h, etc
As of March 2014, there is a Claro plan for 2 pesos per day ($0.20) you get 10MB of data at 3g speeds (which is not much), and unlimited data on edge thereafter. It is not the fastest option, but it certainly one of the cheapest and seems to work just fine for basic maps and social media, not for VOIP.
5 hrs $9
1 day $10 (upto 1GB)
7 days $59
to activate send an SMS to: 226 with: DIA
1 day $10 (up to 1GB)
Special offer: 1 day $1 (first 10MB download at regular speed, next data at 64Kbps)