While you can buy health packs at health stations for $10, you can get them for free by simply smashing the machines with your wrench. After a few hits, between 1-3 health packs should lie on the floor for you to grab, for free.
Atrakinti: Good Ending / Bad Ending
There are two possible endings for BioShock that depend on how you treated little sisters throughout the game. If you choose to "harvest" more than one little sister, you will get the bad BioShock ending. If, however, you "harvest" no more than one little sister but "rescue" the others, you will get the good BioShock ending.
Patarimas: Big Daddy Battle
In order to do this, you need the Hypnotize Big Daddy Plasmid and the Natural Camouflage Tonic. All you have to do is use the Hypnotize Big Daddy Plasmid on a Big Daddy so that he thinks you're a Little Sister and protects you. Now here's the fun part - simply find and attack another Big Daddy and your Big Daddy will attack it to protect you.
Patarimas: Sander Cohen
About halfway through the game, you meet Sander Cohen, this crazy artist dude. When you finish the level, you can just leave him or kill him. If you kill him at that point, you can't get one of the Achievements "Find Cohen's Room." A while later you will stumble onto Cohen's apartment. If he's alive, two Splicers will be dancing in the main room, with Cohen watching from his locked private room. Kill the Splicers and then Cohen comes out to fight you, thus unlocking the door and allowing you to earn the Achievement.
Patarimas: Big Daddy Kills
When fighting a Big Daddy, use armor-piercing rounds, as they will deal considerable damage compared to regular rounds.
Patarimas: Security Drone Manipulation
Use a blast of the Electric Shock Plasmid to temporarily disable security drones before you do anything else in a room. Then, run up to them within five seconds and hack them!
You can hack while the game is on virtual "pause." You'll have security drones on your side for the rest of the time you are in a fight after doing this.
Patarimas: Big Daddy Kills II
Once you get the Grenade Launcher and the Proximity Mines, this technique can be employed. Find a red fuel tank (all over the place), and cover it with about 6 Proximity Mines or so.
Next, use Telekinesis to lift the massive explosive device and hurl it at a Big Daddy. This deals massive damage, leaving you with minimal effort to finish the job. Just be careful not to have the bomb blow up before you get there.
(The launcher upgrade that deals no damage to you is a great thing to have just in case.)