iPhone Is there any good tweaks out there?

[EarthMLG]

Is there any good tweaks that are for an iPhone 4 that wont slow down the phone?

 

[Dalton63841]

I use Bitesms, Zephyr, IntelliscreenX, Switchy, Gridlock, and Tetherme. None of which slow my phone down at all. Oh also, AkAuto3G. That last one has significantly increased my battery life.