I'm not an expert, but the following criteria seem to limit your selection a bit:
Originally Posted by David in PA
light-weight, not too bulky, and reasonable cost
My non-expert input is to consider a high-quality headlamp. Rather than adding a component to your bike, why not just dual-purpose another important piece of gear, that being a flashlight/headlamp. There are versions available that throw a pretty good spotlight out far enough for some riding at night. You wouldn't want to rely on it at 40 mph on a long downhill, but for cruising on the flats should give you enough visibility to ride safely.
Seems to me a dynamo system adds weight and bulk that you say you don't want, not to mention being another piece of gear to install & maintain. How often will you need that vs. a headlamp?
Also note that the good (meaning bright) headlamps will, by necessity have more batteries. Some people don't like having a lot of batteries on their head, or on the front of their head, so consider what your preferences will be in that department.
Lastly, it finally occurs to me that most headlamps will be incompatible with helmets. If you plan to ride helmeted, you may require another solution.