There doesn't appear to be any cheat codes for the game that I can find. However, if you defeat Nemesis on Hard Mode he will drop something that gives you benefit.
First Kill - Eagle Parts A
Second Kill - Eagle Parts B
Third Kill - First Aid Spray Box
Forth Kill - M37 Parts A
Fifth Kill - M37 Parts B
Sixth Kill - First Aid Spray Box
Seventh Kill - Infinite Ammo for One Weapon
It appears as though you must beat the game several times, and on different difficulties, to unlock everything.
In reference to the link that you have added: What you are seeing on that website would be Hex Editing saved game files to give you items or change things around. It is much easier to hex edit saved game files with the PC version of the game than the PS version. The two versions share the same gamesave file format, but it would require much more effort to move a game save between your Playstation and a PC.
No, there aren't any cheat codes in the Xbox 360 version of Mass Effect 3.
If you're having trouble with money or combat, you've got several options. At any point you can turn the difficulty down in the options menu if you think the combat is a bit too challenging. Further, the more you explore the galaxy, probe planets and scan systems, the more credits and other items you'll acquire.
If you do this early on in the campaign, you should have plenty of resources and find yourself having an easy time as you continue.
Further, if you download and install the free Kingdoms of Amalur demo, you can unlock a couple of bonuses in Mass Effect 3 - one is the Chakram Launcher, which is kind of a super-powered charge attack assault rifle, and the other is a unique armor set you get from the beginning of the game. Both of these could be considered somewhat of a cheat. :)
Best Answer
Here is a cheat to unlock all vehicles. While on the screen to choose your vehicle, type in:
to unlock them all.
I found this via searching, although the original source is in French. I don't know if this works, but it is the only cheat I found on the Internet.
For a walkthrough on how to unlock specs in the normal way, here is a guide on IGN (too long to copy content here).