What was the gift from the Dr after saving the little sisters?

For every 3 little sisters you save you receive a gift, which is located at the first Gatherer's Garden you come across after receiving the message. The gifts you receive are based on the below list (source), with you receiving the next item on the list for every 3 sisters you save (starting with item 1).

1. Neptune's Bounty (1st LS): Hypnotize Big Daddy Plasmid; 12 Armor-piercing Pistol Rounds.
2. Arcadia (1st LS): Safecracker Tonic; 12 Electric Buck.
3. Fort Frolic (1st LS): Hypnotize Big Daddy 2 Plasmid; 4 First Aid Kits.
4. Hephaestus (1st LS): 4 EVE Hypos; 6 Proximity Mines.
5. Olympus Heights (1st LS): Armored Shell 2 Tonic; 12 Incendiary Bolts.
6. Apollo Square (2nd LS): Prolific Inventor Tonic; 150 Liquid Nitrogen.
7. Point Prometheus (3rd LS): 100 Antipersonnel Auto Rounds; 4 First Aid Kits.

Therefore the gift you will receive this time is:

Neptune's Bounty (1st LS): Hypnotize Big Daddy Plasmid; 12 Armor-piercing Pistol Rounds.