Depending on what you want to accomplish, and obviously your budget, there is certainly something wonderful in R. Check out Rattle for R and Revolution Computing.
I am a big fan of SPSS and, unfortunately, have not used their Modeler package, but it seems worth considering. I used SAS Enterprise Miner, and although it is powerful, I am not a big fan.
I didn't do much with Weka, but I found that RapidMiner has a steep learning curve, but it has a lot of features.
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