I've found that cold cathode compact fluorescent light bulbs work great for lighting gardens and walkways. If you've ever gotten home late at night with no sun out, you've probably noticed how much nicer it would be with light bulbs illuminating the way. It's easy to do, and doesn't cost a lot of money. While I prefer cold cathode CFLs, there are other options available.
One such option would be solar lights; they are a renewable lighting source that works great in open areas. They are the most simple and easy to install. They're self-contained; all you need to do to install them is stick them in the ground! The sun charges their power sources during the day which allows them to provide decent lighting throughout the night. One auxiliary benefit of their fairly low level of light output is that you don't have to worry about light pollution.
The power sources recharge automatically just by being in sunlight, but because they are powered only by relatively small batteries charged by the sun, their light output is low. Nonetheless, if you're in an area with low or no light pollution, it's plenty of light. If you're in a more urban area with more light pollution, you may want brighter lights to set your garden or walkways apart.
For brighter lighting that still doesn't take a lot of energy, you should get cold cathode compact fluorescent light bulbs. Their benefits include instant-on full brightness, cold weather functionality (they work in as low as -10 degrees F), higher durability than standard compact fluorescents, and high lumen output from a small light bulb. Because they must be powered by an electric line they take a bit more to install, but I've found the extra work worth it. I recommend cold cathode compact fluorescents for any garden or walkway lighting you may need.