Another Summonbro! \o/
Another nice thing you should track down is the Liches Reliquary: This thing has a nice bonus of a HP failsafe should you take fatal damage and offers some massive summon buffs. It requires a few things from the blood moon, the essence of stars, and a grisly trophy from the Dungeon, but can be completed as soon as you get access to the Dungeon.
A second goody can be found in the Jungle, called the Hive Mind. Use it before summoning your minions and turrets for a suitable buff to them!
Beyond that, the Starfish Wand, Thunderbird Staff, and the Expert item from Beholder, there's not much else for summoners pre-Mecha tho. There is a Silk armor cap that allows for starting-game summons and of course the Life Bloom, gained with Cloryphil and grinding out the Jungle for the required second goody.