Attribute Summoner is a series of six Level 4 Effect Monsters with 1400 ATK who, when they're destroyed by battle and sent to the Graveyard, allow the player to Special Summon a monster with 1500 or less ATK and the same Attribute as themselves, including a copy of themselves, from the Main Deck.
Since there is no Level restriction, "Mystic Tomato" can Summon very powerful DARK monsters like "Yubel" or "Earthbound Immortal Wiraqocha Rasca" (though it will only have 100 ATK). You can also Summon "The Dark - Hex-Sealed Fusion" to use as a Fusion Material Monster.
Since both WIND and FIRE monsters have Level 4 Tuner monsters with less than 1500 ATK ("Top Runner" and "Flamvell Magician"), both "Flying Kamakiri #1" and "UFO Turtle" are good to build a Synchro Deck around. Summoning "Hand of Nephthys" with "Flying Kamakiri #1" can easily summon "Sacred Phoenix of Nephthys" with another monster as Tribute.
"Shining Angel" can Summon "Honest", which can return itself to your hand. Special Summoning "Silent Swordsman LV3" and Leveling Up to "Silent Swordsman LV5" on the next Standby Phase would easily net a 2300 ATK monster that's unaffected by the opponent's Spell Cards.
"Giant Rat" can Summon "Ancient Gear Engineer" or "Enraged Muka Muka", which are Level 5 monsters, and "Castle Gate", a Level 6 monster, meaning it could be useful for Xyz Summons. It can also summon "Superheavy Samurai Big Benkei", whose effects would switch it to defense immediately and give you a 3500 beater.