If you use Linux and you need more than two audio inputs,
There have been some really good deals as of lately for used M-Audio FastTrack Ultra 8R:
From what I understand, there are problems with using it with the latest version of MS Windows. So Windows users are getting rid of them for a fraction of what they cost new.
Works great and supported by the Linux kernel using alsa_mixer or DAW(including Renoise) for a control software.
I don’t know about how well it is supported on Macs. M-Audio doesn’t support it anymore.
I got one for cheap on Ebay in the US.
This allows me to keep retro synhs and mic inputs routed for easy synth/effects return, sampling and multi-track audio recording.