I seem to have landed myself in a no-mans land with regards to A/D converters. There are plenty of chips out there, and if I had cared to design my own hardware, I could have gotten 16 bits at 1 megasample from a chip like the AD7677.
I am however, not really into PCB design, and the prospect of doing a PCI bus card is totally out of scope. Instead I looked for an existing product which could do the job at a reasonable price.
And in fact plenty of products exist, but either they stop at 330 kilosamples per second, or do 20 megasamples per second and cost a fortune.
The low-speed cards seems to be built to measure stuff, and act on it, temperatures, quardratures, optics that sort of stuff. The fast cards seems to be aimed at an "oscilloscope" like application where some trigger event starts/stops a capture and you capture just that time segment into the computer.
What I need is slightly different, I want to continuously capture the data, perform a minimum of processing on it in real-time, and then at a more leisurely pace, examine the signals and act on them.
In the end I managed to find a card I could persuade to do what I wanted: PCI-9812 from Adlink Technologies. This card will sample up to 20 Msps at 12 bits and has sufficient on-board FIFO that the rather simple-minded PCI bus-master engine can be used to effect continous capture at 1 Msps, and probably more.