Yep, been there several times. There are several things I feel help me find back to the fun of shooting. I think they've ll been covered above, but...
- Go different places. Doesn't have to be across the world (but could be, of course), just taking a different route to work can be inspiring.
- Take a break. Just leaving the camera at home for a while usually make me want to start again.
- Buy something new. Yes, it works, but doesn't necessarily last for long.
- Find a photo buddy. Going on a photo walk with someone can be very inspiring.
- Make a small project for yourself. Could be joining a challenge like the Single In, or Daily In, or just go out to find yellow objects, or triangles, or... fountains?
That last point, though... I've found that for me three months of Dailies tend to burn me out and I need a break from photography. I guess we all work in different ways