Centering object in workspace.

[Richard Harrington]

Which app

[Vincent Rosati]

In Illustrator, select the Rectangle tool (M) and click on the artboard. You will be prompted to enter object dimensions. Enter dimensions that are the same as your artboard, such as 8.5″x11″ for a letter size document.
You’ll have to group your target object, so you’ll lose layering. Next, select both your grouped target object and the registration object (the new rectangle you created), open the Align palette and click the Horizontal Align Center and then the Vertical Align Center buttons.
Now, with View/Smart Guides activated, click any corner or edge of the registration object and drag it to the appropriate edge/corner of your artboard.

In Photoshop, select the Rectangle tool (U) and size it to fit the artboard using the Move tool (V), with View/Snap enabled. This creates an object with crosshairs in the center. Enable View/Rulers, than click both the vertical and horizontal rulers and drag guides to the crosshairs. Your target object can now be snapped to this centered coordinate.

[Scott Davis]

Photoshop.

[Jason Milligan]

This assumes you are using one of the more recent versions of the apps-

In Illustrator:
In the ALIGN panel, choose “Align to artboard”
Then click the horizontal and vertical align buttons

In Photoshop:
You will need a layer the same size as the canvas.
Select the layer you need to align, then shift (or command/ctrl)-click the layer the size of the canvas. As long as you have the selection tool selected (the black arrow-shortcut V), you will see alignment options available at the top of the screen. Click the horizontal and vertical alignment buttons.