I give myself a bunch of different challenges. For instance, one day I can only shoot something with the color blue in it. Another day I will only shoot vertical shots, or "Dutch" angles. Here are some other subjects, or conditions you can set for yourself.
Cars, buildings, animals, kids, self portrait, movement, freeze the action, water, reflections, horizons, close-up, happy, lonely, danger, trees, fruits, looking up, looking down, black & white, the workplace, co-workers.
How about a travel magazine type photo spread of your backyard, or local park.
One other "exercise" I do is when I leave the house for work in the morning, I always have my compact digital camera with me, and I can't go home until I have taken at least one shot that I would be willing to show to someone else. This keeps me constantly looking at the world as a photograph. I can be sitting at a red light, looking at a building, and instead of staring at it blankly, I'm looking at it to see if there is an interesting angle. When you force yourself to take at least one good photograph a day, looking for that one good shot never leaves your mind, and you will be pleasantly surprised at what you will come up with. The beauty of digital is that is something doesn't work, you erase it and try again.
One last tip. Log on to a site like Flickr, browse some of the categories you will find there, study the images that impress you the most, what angle did they use, time of day, composition etc., then go out and try to replicate it. The best way to learn is by studying those better than you.
Happy shooting.
PS I have assembled lots of videos from amateurs and pros alike that
you can see at www.photography-help.com