Well, I've seen many YouTube videos with admins nocliping around. Does anyone know a plugin that you can noclip?
A PLUGIN that allows you to noclip? No, I don't know of any that would easily allow you to noclip. Physics stuff like that is handled clientside, and therefore would require a client modification.
Like @AgentKid said, you install a client hack. I have a flying hack on my client, makes for easy administering when you can whoosh around.
That's flyhacking, not noclipping. Noclip is when you disable the clipping on the client (physics don't apply normally) so that you can pass through blocks. Flying is flying. There IS a plugin that allows you to fly around....sorta....basically when you jump, it places a 5x5 glass square beneath you, and as you walk it moves it so that you can sorta fly around. It's called MagicCarpet.
Zombe Mod Pack OR MagicCarpet. Some Mods allow you to do xRaying etc but the downside is you can't place/modify blocks in the server if you have them installed.