I'm sorry but I didn't find this entirely useful. Are they allowing us to use the raw data sources? If so, I wasn't able to download anything, just clicked through and found more documentation.
It looks like this aggregates links to other dataset sources rather than being a source itself.
I'm impressed, this will be super useful. I spend a decent amount of time looking around for datasets, and it's harder than I would have imagined.
Finding out about Quandl is alone a pretty big victory.
There are a lot of awesome data sources out there that are currently being put up for public consumption by small independent teams, one example being DrugCite.com which takes the FDA AERS (Medication Side Effect) data and lets you search by drug name, side effect, ect. then sort it be age and gender.
For people looking for additional data sources, AWS has many public data sets available - http://aws.amazon.com/datasets