In the last weeks I followed an idea to measure current without the need to cut the wires or even open a pcb trace. The solution i came up with is a hall effect based measurement.
I wrote some more about it in an article here: http://avrs-at-leipzig.de/dokuwiki/en/prokekte/fluxprobe
If you do not like to open the full arcitle here you can review the basic schematic as well as to see a foto of my first prototype:
For more detail: Building a current / flux probe for contactless measurements