I'm am looking for some datasets that contain data about a specific disease - any disease (preferably with several known treatments). I need such datasets, that contain information about the patients, the treatment/medicine that they received, and the treatment's outcome. I've tried to look everywhere, but couldn't find anything.
ClinicalTrials.gov contains lots of information - not just for the US, but also for the other markets important to "Big Pharma".
The blog of drug discovery chemist and blogger Derek Howe In the Pipeline (it's now a column of Science magazine) contains in-depth discussions of interesting recent discoveries. Each of his blogposts about clinical trials contains numerous links to papers and, if you dig deeper, data.
If you want a somewhat standardized access to datasets from experiments, get familiar with the Bioconductor Project that was developed by the R community. Example: > 80 Human cancer datasets
(Bioconductor specifies how code and data should be packaged together, to encourage data sharing and improve reproducibility).