Orianna

Orianna and Lee Sin combo in soloq is dangerous, she gives you lots of mobility / shielding and often (from my experience) has prio, which lets Lee Sin up for early crab / fight

Lulu

Same here with both mobility and shielding / healing, Lulu and Lee Sin is a monster duo, if you are already ahead as Lee sin and your Lulu plays around you you can win many games with the amount of help your Lulu gives you.

Bard

Bard, the king of Roams have an insane synergy aswell, especially setting up ganks / invades with his portals, aswell as setting up for Lee Sin to ult targets with Bard ult.

Thresh

Thresh can also many times be a saviour of yours, even though he doesn't usually give mobility (unless shyrelias) His Lantern / Hook can set you up for so much during the games and can be a huge factor to you winning the games as Lee Sin.

Yuumi

Last enabler, Yuumi and Lee Sin with Goredrinker / Steraks should have an easy time (if ahead) Yuumi enables so much for Lee sin with her insane healing, shielding and mobility aswell as giving Lee Sin the extra adaptive force, can definitely 2v8 games if good mechanical players.

Kassadin

Vladimir