I'm pretty impressed with the TC Electronics tuner. It can tell you which string(s) is/are out of tune from a strum, and it can store preset tunings from your computer using a USB cable, if you're into that.
I had success with the green Line 6 delay modeler pedal and its loop function. Lots of useful settings, nothing too heinous like what you find in other Line 6 pedals, but it's not true bypass and you already have a delay. Friends of mine swear by the Boss looper, FWIW.