League of Legends items that grant allies bonuses

Here are all I can recall currently.

• Locket of the Iron Solari has an active shield for allies.

• Captain enchantment for any type boots will give bonus move speed to nearby allies. -Removed in Patch 6.9

• Ardent Censer gives allies that you shield or heal bonus attack speed and on hit magic dmg.

• Athene's Unholy Grail heals allies that you shield or heal based on the stored damage you have done to enemies.

• Zeke's Convergence gives the ally it is bound to bonus auto attack magic damage when it procs via ultimate cast.

• Shurelya's Reverie gives a brief movement speed buff to nearby allies.

• Face of the Mountain grants the target ally a shield based on a percent of their maximum HP. Removed

• Elixir of Iron causes your champion to leave a path that grants allied champions bonus move speed.

• Abyssal Scepter causes your enemies to lose magic resist, which effectively grants your allies bonus magic pen. Removed

• Abyssal Mask causes your enemies to take increased magic damage, which effectively grants your allies a magic damage buff.

• Mikael's Crucible Removes all stuns, roots, taunts, fears, silences and slows on an allied champion

Non-Items

• Windspeakers Blessing Gives allies that you heal or shield bonus magic resist and armor. This is one of the keystone masteries in the cunning tree. Removed