The card with the lowest HP would actually be the early Mysterious Fossils. http://serebii.net/card/fossil/062.shtml 10 HP as you can see.
http://www.pokemon.com/us/pokemon-trading-card-game/database/advanced/?cardName=&cardText=&basic-pokemon=&evolvesFrom=&format=unlimited&hitPointsMin=0&hitPointsMax=30&retreatCostMin=0&retreatCostMax=5&totalAttackCostMin=0&totalAttackCostMax=10&particularArtist=&searchDatabase=Search Database&sort=Position
those are all of em! because the LOWEST Pokemon card HP is 30. and there are alot of magicarp and baby Pokemon! =P