is Open Source, has an adequate GUI, many different kinds of algorithms available, and a "knowledge flow" visual designer for you to chain it all together. I've used it in a few personal and professional projects to find things like which variables most strongly influence an outcome, decision trees, derived formulas and expressions that accurately predict outputs from inputs, and various kinds of data visualizations for clustering data samples. Code is in Java so I presume you could embed it within a system to automatically perform analysis and swap algorithms on the fly. Best of all, since this is software under your control, and not a Corporate-offered service, your valuable data never leaves your control.
I think WEKA already did a lot to make these kinds of data analysis accessible as Microsoft is aiming to do. No matter who provides it to you, there is something totally awesome about being able to click a few buttons and get some interesting results to munch on.