Databases
Barabási, A.-L. and Toroczkai, Z.
Barabasi's network data collection
Set of complex networks studied on works by Albert-László Barabási and collaborators. p>
NeuroMorpho.org
The largest dataset of 3D digitally reconstructed neurons from over 60 institutions around the world. p>
Batagelj, V. and Mrvar, A.
Pajek networks data sets
Complex networks files compatible with the Pajek software. p>