I was thinking about the new Sony lenses only,
like the CZ 16-80, you can't use it on tha a900,
also the 18-70, 18-200 and the 18-250.
The cz from around 1500 euro fit well.
Actually you can use DT lenses, but images are automatically cropped to 11MP (there's an APS-C mode)
I guess if you are looking at buying superzooms, the a900 will not be on your shopping list. There is little point in using APS-C lenses on the a900, you are much better of buying 3rd party FF lenses.
And like most a900 owners, the 3rd party lenses will be stop gaps until they can buy the real deal (16-35,24-70,70-200 f2.8 SSM) or maybe the lens covers a focal length they don't require such high resolution.
There are lots of stop gaps BTW, and a lot of them perform very well. Tamron 28-75 is a cracking lens on FF. My KM 17-35 (same as Tam 17-35) also performs very well. But put a top end lens on the a900 and it really does shine.
e.g.. took a test shot with the a900 + CZ2470. This is the lens wide open at f2.8:
This is the full size image:
This is the cropped image:
100% crop: http://farm4.static.flickr.com/3414/3345868033_10a5ccf7d5_o.jpg
Note that when looking at the a900 images at 100%, as most monitors display at 75dpi - the image size would be roughly (if I remember correctly) 1.5m x 1m