Hi, I am new in this forum. I am very interested to invest my time and some money in a data-logger development based on Arduino. I think that the problem must be divided into some steps: how to interface sensors to arduino input, that can be solved with easy electronic circuits;
how to get arduino writing data on a SD card or USB pen drive;
how to get enough power autonomy for long data logging (months).
In fact I think to use this sort of device to monitor slow environmental phenomena (i.e. wine cellar temperature :)).