First,
Root your phone.
Then, Install Rom Manager from Play store and use it to install Clockword Mod Recovery.
Use it to create a Nand backup of your phone. This will backup everything. If you were to restore from this backup your phone would basically be the same as it is right now. Make said backups whenever you are about to do something that might be considered stupid. You can always come right back to where you were before!
Next, Download Titanium Backup Pro. Use it to freeze these apps so they won't take up memory or CPU cycles in the background:
AllShare Cast
AllShare Cast D..
AllShare Play
AllShare Service
ChatOn
Flipboard
Game Hub
Google+ (unless you use it)
Kies Air
Kies Air Wifi
Media Hub
MobileLife (or your carrier equivalent)
MobileLife Contacts (or your carrier equivalent)
More Services
Polaris Viewer
S Memo
S Suggest
S Voice
Samsung Apps
Samsung Push Service
Talk
TalkBack
Visual Voicemail
Voice Recorder
VPN Client
Yahoo Finance
Yahoo News
I don't use the S programs (voice activation) because they are extremely battery taxing. Especially if you set it to wait for your command while in sleep mode. It basically stops it from actually going into sleep mode.
Don't waste time installing ROMs... They all suck and none of them are actually perfect. So one might have camera issues while another has force close issues. They won't make your phone any faster.
With all of those apps (and any others that your carrier might have installed) frozen your phone will act like an Android phone instead of having all of the other bullshit. It will still do the Samsung stuff like stay on when you are looking at it without killing the screen on a timer. It just won't have annoying shit going off trying to get you to be a social fuck-tard.