I currently use SBPowerAlert, Activator bound to sleep short hold, to display my wifi IP address. It can display SSID, available storage, and free RAM too. You could also use Cloaky to display it on the status bar in the clock text. WiCarrier was great pre iOS7 as it replaced the carrier text with your IP. Net Analyzer is a great App Store app for scanning networks, and it shows you your IP address.