Summer School On Symbolic Computation (July 2007)

GAP Workshop (September 2007)

Applicable Algebra & Computer Science (February 2008)

Conference on homology and homotopy (March 2008)

Conference On Computational Group Theory (August 2008)

Algebra and topology: methods, computation and science (June 2010)

Computer algebra in algebraic topology and its applications (June 2010)
(I'm a guest editor of the AAECC volume containing this conference's proceedings)

Summer school in algorithmic mathematics (August 2010)

Mathematics, Algorithms and Proofs (November 2010)

Oberwolfach meeting on computational group theory (31/7/ - 6/8/2011)

SIAM Conference on Applied Algebraic Geometry (AG11), October 6-9, 2011, Raleigh, North Carolina, USA.  (In particular, the Exact Linear Algebra session.)