Disable if you don't use VPN, Virtual Private Networks (if you don't know what it is, disable it).

Disable if you don't use The Cydia Autoinstall feature, which automatically installs debs placed in /var/root/Media/Cydia/AutoInstall upon boot.

Disable if you don't use spotlight.

Disable if you don't use push notifications.

Disable if you don't use the iPhone's Internet tethering/personal hotspot feature.

Disable if you don't use MobileMe services.

Disable if you don't use Exchange services or Gmail.

Disable if you don't use obliteration features. Obliteration allows you to wipe your device from your device through Settings -> General -> Reset, remotely through Find my iPhone, or through the "Erase all data on this iPhone after 10 failed passcode attempts," etc.

Disable if you don't need to import contacts from your SIM card. If you've already imported your contacts from a SIM card, you can disable this.

Disable if you don't want transparency effects, which appear when opening the multitasking switcher from the homescreen and opening folders. Transparency effects cause folders and the multitasking switcher to open slower.

Leave this on if you don't need retina images (why would you on a non-retina device?). Retina images are only used on retina devices (iPhone 4, iPod Touch 4g, iPad 3rd Gen or newer). Removing them will free space and save some ram.