Lucky charms are life-gaining artifacts, such as the ones originally from Alpha — Ivory Cup, Crystal Rod, Throne of Bone, Iron Star, and Wooden Sphere. The original lucky charms were printed in every Core Set from Alpha to 8th Edition. Another similar artifact was Soul Net, which triggers whenever a creature dies.
Antiquities lucky charm
A life-gaining artifact following the theme of the original lucky charms, Urza's Chalice, was printed in Antiquities. This artifact triggers on artifacts, rather than colors. It is so far the only lucky charm that's common rather than uncommon. Also, an artifact that imitated Soul Net's death trigger, Tablet of Epityr, was printed.
Darksteel lucky charms
Another cycle of life-gaining artifacts was made in Darksteel — Angel's Feather, Kraken's Eye, Demon's Horn, Dragon's Claw, and Wurm's Tooth — were printed in Darksteel, and they have been reprinted in every core set from Ninth Edition to Magic 2012.
These updated versions don't require the owner to pay mana in order to gain a life, at the cost of having the artifact cost more. It was felt this would work better in a core set, which is targeted at newer players. At the time, core sets didn't have any new cards, only reprints, so room had to be found in an Expert-level expansion. Darksteel was finally the set to have this cycle see print because of the artifact heave theme of the Mirrodin block. 
Time Spiral lucky charm
Scars of Mirrodin lucky charm
Following the theme set in Darksteel, Scars of Mirrodin improved on the original artifact lucky charm that was printed in Antiquities. Golem's Heart used the same change as the Darksteel lucky charms did: taking out the activation cost, but making it cost more.
Magic 2014 Staves
For Magic 2014, a cycle of uncommon artifacts costing was introduced, more than the Darksteel cycle and more than the original cycle — Staff of the Sun Magus, Staff of the Mind Magus, Staff of the Death Magus, Staff of the Flame Magus and Staff of the Wild Magus.
Each staff allows a player to gain a life both when casting a spell of the color, or when playing a land with the basic land type associated with that color. The staves only trigger when the controller plays a spell of the appropiate color instead of any player.
- Mark Rosewater. (July 31, 2014.) "What do people mean when they say "lucky charms" as of late?", Blogatog, Tumblr.
- Mark Rosewater. (December 10, 2007.) "What Do You Know, Part II", Daily MTG, magicthegathering.com, Wizards of the Coast.