Yeah as tim said street photography can be pretty awesome.
Animals can also be good if shot well.
Nature is always a wide topic to shoot.
Even just if you can sit across from a bustop right
and you sit there all day! and take a photo of each person that sits at the bus stop,it can be pretty intresting because you wonder whats going on in there lives.
You could always go simple. Pick a color and walk around town looking for it. When you do find something of the correct color really try to get the best composition you can find, it might not be the best pictures in the world but as a set they'll fit together fairly well. And I think it helps not only getting your eye used to looking for specific things but also visualizing compositions of subjects you wouldn't normally try photographing. You might surprise yourself with one of the shots.
OR
Do something along the lines of the "Roaming Gnome" concept.
DON'T USE A GNOME though its been done too much use just any unique object that you have.
Use something that you can carry from place to place and photograph it in front of various local landmarks.
Hope i gave you some ideas.
