This is basically the plugin by weasel5i2, all credits to him. I just added support for Minecraft 1.2.3 and switched to PermissionsEx

Wings - Simple Flight
Version: v1.4

This plugin lets you fly around. Simply hold a feather in your hand and right-click with it to toggle flying and hovering on/off. First click will enable flight mode. A second right-click will switch you into hover mode. A third right-click will switch off flying and you will fall to the ground (without damage, as long as you're still holding the feather!)

You will fly in the direction you're facing, so if you're going to hit that mountain, well.. PULL UP!! PULL UP!!!

Features:
Flying around in the sky like some crazy bird.
Hovering! (mostly..) - while hovering, hold down SHIFT to move yourself upwards.
Permissions node:
- 'wings.fly'

Configuration:
The configuration is located in plugins/Wings/Settings.ini. The file looks like this:

hoverMultiplier=0.0012410253
hoverBoostMultiplier=0.00555
allowOps=true
flyingEatsFeathers=true
defaultFeatherAmount=500
flightSpeed=1.0

* hoverMultiplier: The vector amount to achieve the player hovering effect. Your mileage may vary depending on how this is set.
* hoverBoostMultiplier: The vector amount to get that extra upward boost when you press SHIFT whilst hovering.
* allowOps: Allow Op users to fly, regardless of their Permissions setting.
* flightSpeed: The amount to multiply the flight vector by. Don't set this too high or you may end up extremely far away from your intended destination!
* flyingEatsFeathers: (disabled by default) - Set whether or not flying and hovering will consume feathers. Note that the feather must be held in the FIRST hand inventory slot #1 (at least until I can figure out how to get it to see them elsewhere in the player's inventory)
* defaultFeatherAmount: This sets how many ticks each feather will last before being consumed. On my server, the default 500 setting makes them last approximately 15-20 seconds each before disappearing from the stack.