jokkemokke:
I think the I/O options on the Raspberry Pi are a bit limited, since there are no analog inputs or outputs.I guess what I am looking for is a Raspberry Pi with the same I/O options as the Arduino, but I don't know if something like this exists.
Hi,
Since you mention the RPi, even if they don't have analog I/O, that's functionality you can add in the same way as adding extra analog inputs to the Arduino. Chips like the MCP3008 or similar will do that for you - and as you identified you might need some logic level shifting. Alternatively, moving to digital sensors would eliminate the need for your analog inputs too. Adding a Gertboard to the RPi provides the additional IO from an ATmega MCU onboard (if that fits the budget) or of course you've already got an ATmega on your Arduino...so you could utilise your Arduino to interface your sensors to your RPi.
Since your design brief is quite open, anything will do - I only stuck with the RPi since you mentioned it.
Sorry for the Cheshire Cat style of answer.
Geoff