BITalino can synchronously and simultaneously sample up to 6 channels.
There are 4 main channels with 10-bit, and 2 auxiliary channels with 6-bit. BITalino also has 4 digital inputs (1-bit) and 4 digital outputs (1-bit) sampled and triggered at the same rate.
All channels are exposed as holes on the board. In the Plugged version you have the 4 main analog channels available as RJ22 sockets, as well as the 4 digital input and outputs (in this case the socket is shared).
Note also that you can always cascade multiple BITalinos, enabling you to expand the number of channels. Provided that they have digital ports connected between them you'll be able to have a common time reference from which to synchronize the data from each device.