Many of you who are wishing to create a Minecraft Custom Client want an FPS display somewhere in game. It doesn't matter why, or where, you just want to copy and paste stuff in it and call it yours. Well, here it is.
Code:
int fps = Integer.valueOf(Minecraft.debugFPS);
Firstly, we create an integer (int) which would be called fps. This integer uses already made counter of FPS, therefore making this really easy to do.
This calls the void from Minecraft.class.
Code:
var8.drawStringWithShadow("\2472FPS: " + whatever your integer name was, x, y, hex colour code);
Then we call the drawString void. Notice how for 1.5.2 we use var8 instead of fontRenderer. So we use var8.drawString to draw our string (text).
In the brackets we have our string "FPS: " and our int + fps. We then add the x and the y coordinates and our colour code. After closing the bracket add a semicolon.

My client uses x and y coordinates so that if you try to resize the game, the FPS stays in the bottom right corner and not somewhere lets say, 420, 400. You can use simple math to make your string adjustable.
To do this, you're going to have to call an integer from GuiMainMenu.class
Code:
GuiMainMenu.width - 50, GuiMainMenu.height - 12
This grabs the current width and height of the, lets say, JFrame or whatever minecraft uses.
Skid unfriendly-ish.
You should all know where to place all of this. But if not, it is supposed to go in GuiInGame.java