Safety is the most important aspect of babywearing. Here are some links regarding recalled baby carriers. Please note the date and specific models-- many carriers such as Beco and the Maya Ringsling are perfectly safe assuming they are not part of a certain batch.
A list of recalled carriers:
Search results for baby carrier on the CPSC recall site:
The Babywearer index of recalls:
The Babywearer explains bag slings and their dangers:
Is My Sling Safe?
CPSC article on Infantio SlingRider deaths:
CPSC article on sling warnings and safety: