I don't know why, but i always find myself really inspired when i play someone else's guitar. I think it's probably a psychological thing; i'm so used to how mine feels and have battered away on it for the past 12 years that it sometimes feels more like a crutch than a thing of passion. But even picking up a guitar a guitar in a shop to mess around on, within minutes i've usually gotten some kinda cool chord progression/riff worked out and a melody in my head to go with it and i run home and get to actually writing it on my guitar.
Otherwise, i'm fairly melancholic anyway so find myself inspired by issues surrounding either my own life or people close to me going through turmoil (cheery right!?

)
I kinda agree with mjb about being more inspired by what i
read than what i
watch, but then again i think it depends on how much it draws you in and how much it engages your imagination. For example, after watching "the blind side" (cracking film!) it left me thinking about a whole bunch of stuff and was compelled to write (but, then again, i work with kids from similar backgrounds so related on a very personal level to the film). However, 4 series of "The Big Bang Theory" has probably distracted me from writing for x amount of hours!
the big thing with reading, whether it be fact or fiction, is that alot of the time it forces your imagination in to gear to bring the words to life and, with some things, those thoughts or feelings carry on after you've finished reading. Again, as another example, the singer in our band wrote a very dark song (which was quite unlike him, he openely admits to wanting to be brian wilson back in the beachboys heyday) and it wasn't until we recorded it and really heard the lyrics that we decided we really had to ask what on earth it was about. turns out he'd read an article written by josef fritzl's daughter about her captivity and escape and it had struck a chord with him so he laid pen to paper.
All of that aside, and maybe i've missed it, but the OP hasn't said whether it's an issue with writing lyrics, music, melodies, or the whole shebang! Again, as an example that many will be familiar with, i've got a shed load of incomplete songs where the music is ready but i've never found the right melodies and lyrics.
If it's an issue with writing the actual music then, as elbandito said, playing with other people can be an amazing way of helping to take basic ideas and gel them into something. Otherwise, learning covers of songs you like can help identify types of chord progressions and patterns, and even teach you new chords or new voicings for chords you already know.