We have under-counter lights in our kitchen that use small halogen bulbs. They run at 120V and consume 20 watts of power (each). In addition to consuming a lot of power, they run hot! I use two of the lights as a night light for the kitchen, and after a few hours, the dishes and lights in the shelves above are warm to the touch.
Almost all of the lighting in our house has been on LED for yeahs, but it's taken a long time for good, small-halogen replacements to appear on the market. One of the under-counter halogens went out last week, so it was a good push for me to do the research to find a suitable replacement. First, I had to figure out what kind of bulb I needed. Bi-pin bulb formats are plentiful and confusing. Fortunately, if you have a digital caliper, you can figure out what kind of bulb you need by measuring the spacing between the pins (full instructions here) and by looking at the pins themselves. Ours turned to be G8 bulbs.
I cost Kakanuo G8 LED Bulb Dimmable G8 2.5 Watt Warm White 3000K bulbs, which run about $17 on Amazon for 6 bulbs. They are wide-angle lights, but only work in one direction, which means that the quality of light will be dictacted by the bulb, not the fixture (reflectors in the fixture will be blocked). My original bulbs were 20 watt bulbs; these are 2.5 watts and use 87% less electricity. The 3000K version this bulb is pleasingly-warm, and outputs wide, even, high-quality light without getting hot.
Left: G8 halogen bulb, installed; Right: Kakanuo G8 LED bulb installed
I'm really pleased with these bulbs, although my fixtures don't dim, so I only see them at full power. If you need a LED bulb that dims well for a particular fixture (especially old fixtures), you might need to purchase a few different bulbs and test them. LED dimming is notoriously finicky. Also, if you want to try to retain any light quality that comes from a fixture's reflector design, you should look for an omnidirectional bulb that matches your original in design.