I visited Versailles in summer for four days and it was great (definatley will visit it the next year too)! We made three very interesting tours through the private rooms of the king and the queen and also of Mme de Pompadour. If there is someone interested in, I could post some pics...
Its true that you can visit the parc of the palace for free, but only under the week. At the weekends there are the Grandes eaux musicales and you have to pay for it. When you're under 26 it's also great, cause then you can visit the palace with the Grands Appartements for free!