I have found this little app from Adafruit to be really handy when I want to ssh into a Raspberry Pi but can't remember the I.P. Works on most OSs.
This can be annoying when you have a bunch of them as a few of us do.
Just click on 'Find my Pi' and it will come up with the I.P. for the near-by Pi.
Use ethernet if it doesn't already have wifi up.