Carnegie Mellon University hosts a repository of UIMA components: http://uima.lti.cs.cmu.edu
Jena University also has started a collection of UIMA components: http://www.julielab.de/content/view/122/179/
A 3-way joint effort by Tsujii Lab, University of Tokyo, Center for Computational Pharmacology, University of Colorado, and the National Centre for Text Mining (NaCTeM), University of Manchester, hosts a repository of type-system-compatible UIMA components, together with testing and evaluation tools: http://u-compare.org