Interesting thing about the aircrafts delievered to the Soviets is their opinion about them. The P-39's and P-63's received good grades, while the P-47 was felt to be a second-grade aircraft, being compared to the Il-2 in the ground attack role. There are also several stories about Finnish pilots meeting (and in some instances downing) Soviet Mustangs, while archive research have shown that the Soviets didn't use any Mustangs at all in combat.
However, the biggest lend-lease item must surely be
this one