Information: We implemented an algorithm to compute a Dirichlet domain for a Fuchsian group with cofinite area.
Here is a link to the (submitted) article.
[math.NT/0802.0196] [PS] [PDF]Here is a link to the demo at the Bristol workshop on Computations with Modular Forms:
[Magma]Substantial optimizations have been made to the algorithm and are being incorporated into the latest version of Magma (V2.17-4). The best way to get these changes is to wait for the new release, or just e-mail me and I'll send you the requisite files.