If don't have much of a green thumb, this Arduino-based monitor lets you know if your indoor plants are getting enough water and light. And even if you don't need the gardening help, it's a nifty little Arduino project.
The Leaf Light, from Instructables user knsievert, uses soil moisture and light sensors connected to an Arduino to let you know when your plants need more water or a spot closer to a window. It alerts you using a multicoloured LED/NeoPixel that glows different colours depending on what it detects. Green means all is well, blue that your plant needs water, orange when your plan needs more light, and red when it needs both light and water. You'll need several components and there's some light soldering involved, but nothing a novice couldn't handle with a little patience.
Leaf Light: An Indoor Garden Monitor [Instructables]