These are a few ideas I have for /client. Haters, leave now.

/client watershade :on:off: | Shades water and makes it reflective of the blocks above it.
/client lavabub :none:low:high: | Makes lava glow and makes lava bubbles come out of it.
/client xray <block> | Makes the block specified invisible. Say it again to turn it off.
/client colors :royal:sleek:new:old:beta: | An add-on to the existing colors. Royal is gold plating with
gemstones over it and Sleek is the New color style, except really smooth.
/client lighting :off:low:medium:high: <hex code color>| A great addition for screenshotters using World of Minecraft. It has three lighting options and if hex code is not specified, it will be white lighting.

And finally, press C to open the chat typing area with /client already typed in. Anyone like? The water-shading and the lava bubbles would need extra graphics added into the World of Minecraft/lib/minecraft folder.