I just wanted to recommend a piece of gear I picked up recently that's really been helping me with my songwriting ideas.
It's the TC Helicon Voicelive 3. It's a little on the pricey side but, honestly, the features they've packed in is pretty amazing.
First of all, it's a vocal pedal that does harmonies. Now, I prefer to stack my own harmonies when I record BUT being able to tap a button and hear harmonies in the writing stage is pretty amazing. And it follows the instrument you have plugged in, so the harmonies will be in key with your instrument.
Then there's the guitar processing side... They've actually included the parameters to create your own amps. Ok, it's not the same as a tube amp singing away in a controlled room with decent mics. But when you dial the tones in right, the emulation is close enough for some pretty decent guitar sounds for recording. It also has an octave effect which I've used for writing basslines on the fly.
Finally, the looper side. This is what's made the unit such a great songwriting device. Say I have a guitar line that i want to build on, within seconds I have it looped and now I can create a bass part or try out some harmonies, or add some drums. For me, it's just been amazing to have all these instruments available to me without taking up hardly any space at all.
Finally, any ideas you like, you can record direct to USB from the unit. Recording demos is such a breeze now. I've even midi's the clock to my recording software so my demo tracks are synced up to the software.