If you are in the market for quantitative investment software, here is a short (but not exhaustive) list of companies supplying it in addition to those recommended sites. Excluded, at least for the time being, are suppliers of market data, derivatives pricing tools, technical analysis, backoffice software etc.
This list may not be complete, so please let is know if you think that there is a name missing from it, especially if it is yours. Let us know too if there are any similar short lists (eg data vendors, back office software) that you'd find helpful