I have a OASE pondovac - it works really well, not inexpensive mind you, but does suck up the rubbish.
My biggest complaint is it only holds 25ltrs of water before it switches off to empty which in some cases isn't on for very long at all and the dirty water left in the pipe then flows back into the pond stirring it up a bit (I find the attachment with the valve to stop this happening prevents the larger items of debris of being sucked up).
But on the whole I wouldn't be without it.
My biggest complaint is it only holds 25ltrs of water before it switches off to empty which in some cases isn't on for very long at all and the dirty water left in the pipe then flows back into the pond stirring it up a bit (I find the attachment with the valve to stop this happening prevents the larger items of debris of being sucked up).
But on the whole I wouldn't be without it.