Hi Stacey,
Wow, there are so many good places to shoot downtown now. If you haven't been there in awhile you'll see that a LOT has changed.
Some ideas:
-Belle Isle is always a popular choice. You can get the Detroit skyline, the area by the conservatory is nice (go around to the back, there's a lovely garden with a pond.) The front of the (now closed

) aquarium is pretty, there are several pretty footbridges (and the main bridge to the island is nice), and there are some other monuments worth checking out. Plus there's a lot of nice woodsy areas too.
-Downtown near the Fox, Comerica park, etc. There are also some alleys around there that make good backdrops and it's populated enough to feel safe.
- Get on the people mover and get off at random stops. Some of the stations themselves are kind of neat.
-The riverwalk is mostly completed and looks great. It's very walkable, there's a carousel, water features, the river (doh), and the area around the RenCen is interesting.
-Campus Martius has been cleaned up and is worth a visit.
-The DIA has a water feature and makes for a nice background as well.