Note for all A-D converters: Modern Macs lack built-in serial ports, so you'll need a USB to serial converter and driver software. The units made by Keyspan (now, TrippLite), specifically the USA-19HS, function reliably with LabHelper. Other brands have not worked well, or at all.
Remote Measurement Systems ADC-1 The ADC-1 (no longer manufactured and rather ancient in its functional attributes) has 16 channels of 12-bit analog-to-digital conversion and six digital I/O lines. It can communicate at speeds of up to 9600 baud, and is limited to sampling rates of no more than 2/sec for most applications.
If possible, get an ADC-1 with the normal
input voltage range (±0.42 volts) and the 50X programmable
gain option on all 16 channels. You can use an ADC-1 with the
gain option on only 8 channels if you are careful to attach your instruments
to those channels exclusively. You can use an ADC-1 without
programmable gain, but resolution will be much more limited.
Since the ADC-1has such a low input voltage maximum (±0.42 volts), you will probably need to use voltage dividers to reduce your instruments' recorder output voltages substantially. Most instruments have output voltage ranges of 0-5 volts to 0-10 volts; some have both positive and negative voltages.
The ADC-1 comes with screw terminals to which you can directly attach
instrument recorder cables. However, you may want to build your own
junction box with connectors that are easier to use.
Note: Because of its low sampling rate, the ADC-1 cannot be used in oscilloscope mode.