Dennis has already mentioned the Astrotrac.
http://www.astrotrac.com/Default.aspx?p=tt320x-ag
The basic Astrotrac is a little more expensive than the Polarie, but is claimed to be able to carry up to 15kg. I have never loaded it up that much, but I have put maybe 5kg load on it with no drama's at all. (Stellarvue SV70ED refractor, Field flattener and Canon 60Da, mounted side-by-side with an Orion ST80 guidescope and QHY5 guide cam)
The only real negative that some people point out about the Astrotrac is the maximum of ~2 hours tracking before the unit needs to be rewound, but that has never been an issue for me. It also has Solar and Lunar tracking rates(a friend borrowed it for the Cairns Solar eclipse), and also has a guide port, tho autoguiding works for RA only, but still better than nothing with longer focal lengths.
My Astrotrac gets borrowed all the time and everyone that has used it loves it and wants to get one, but I have the full kit which is pretty pricey so they keep borrowing that, but I don't mind
Worth considering.