Can someone list some alternatives to IndexTank? We rely on them pretty heavily and this is going to leave us, and I imagine quite a few other companies, in a bind.
IndexTank have already said that they'll open source their code so others can take up the mantle. Another alternative is the excellent open source Apache Solr search engine, discussed elsewhere in this thread.
Sphinx and Solr are both options to consider, and there are few Search as a Service providers that you can use. Flying Sphinx and WebSolr are two of the more popular ones.