Reload Canceling:
The same with most games,in Borderlands canceling the reload animation can often speed up reload times. So basically as soon as the animation begins and the clip is pulled out of the gun or bullets are being put in the gun just hit melee. This can shave a second or two off of reload times, which can be useful in any situation.
Level up before starting the game:
At the beginning when you follow the claptrap through the little intro area you can exit near the end and just keep doing it over and over. It saves the levels and money gained by your character but reloads the same intro area over and over. This is kind of a cool cheat for Borderlands, but most people want to start the game.
Duplicate Items Cheats:
To duplicate items in Borderlands what you do is drop whatever item you want to duplicate on the ground. Make sure you have a friend in the game as well. After this, exit the game without saving and have one of your friends pick it up. Then come back in the game and you will have your item back in your inventory and your friend will have the item he picked up.
Easy Money and Weapons:
Once you arrive in New Haven for the first time head directly to the save point near Scooter and save your game. Once saved, just loot all the chests in town, there are 5 in total. Just keep reloading the game and looting while also checking vending machines for new weapons. This is an awesome way to get free weapons and money in Borderlands.
Eridian Weapon Early on:
One of the characters in your party must be a Siren. Just head back to Fyrestone and kill Mothrakk and a guaranteed Eridian weapon will fall from him. Make sure you lure Mothrakk close though otherwise its easy to lose the weapon in the zone. This is an awesome way to get an early Eridian weapon in Borderlands

GamerStrategy Blog