1 Alakazam (7), 2 Blastoise (7), 3 Chansey (7), 4 Charizard (7), 5 Clefairy (7), 6 Gyarados (5), 7 Hitmonchan (7), 9 Magneton (7), 10 Mewtwo (6), 11 Nidoking (6), 12 Ninetales (6), 13 Poliwrath (7), 14 Raichu (7), 15 Venusaur (7) and 16 Zapdos (6)
Anvil of Bogardan also does a decent Howling Mine impression and would see more play if it wasnt so expensive
It is very good just for the fact it provides any type of energy and also has opponent damage reduction
I was a big fan of Maul of the Skyclaves, which had a very similar feel: White equipment for three mana, attaches for free when it enters the battlefield, four mana to equip, +2 power and flying
The flexibility is the beauty of the mechanic, allowing you to have two different effects on the same card depending on how much mana you have