Where can I find a longitudinal study with a binary response? I've spent the last couple of months trying to find real data (not simulated) of a longitudinal study, but I can't seem to find one. Any topic and time frame is fine, but the dependent variable must be binary, and a few covariables are also desirable. I appreciate any help immensely!
(1) The statistic software R comes with a number of datasets. You can see which datasets are available with the command data(). Here is an overview.

Among the datasets that came with my distribution of R is the dataset Titanic, which includes the binary variable "Survived", which gives information about which passengers survived the Titanic's maiden voyage.

Another dataset, UCBAdmissions, gives information about which applicants were admitted or rejected to UC Berkeley.

The data in both datasets is grouped (by sex etc.). Both are not longitudinal, though.

You can get information on each dataset with ?datasetname, e.g. ?Titanic. Maybe more datasets include binary variables.

(2) As Jeromy Anglim noted, many statistics text books offer an online data repository. Here is the one for Applied Regression Analysis and Generalized Linear Models (2nd ed.) by John Fox. Here is the one for Statistik (7th ed.) by Fahrmeir et al. (in German).

(3) Here is a linklist to free datasets, here is another. I guess there are more.