[TheJoshu]

After playing with Photoshop for years and years, I still have one issue I've never dealt with... I do not know how (if there is a way) to align elements within a document. For instance, if I have an image inside the document, I can only center-align it by eye or by selecting the negative space to the left of it and fiddling with it until it equals the negative space to the right. There must be a better way. What obvious feature am I missing this time?

Thanks as always.

[dampeoples]

Turn the grid on. I use elements, so your menu may be dirrerent, but it's under View>Grid
There's also a snap to grid option you can select if you don't need fine placement

[gadster]

Depends what version you are using.

This works for 6. If you make the 'background' a layer, click on it, then drag a guide out to near the centre, it will snap to the centre of the page (do this before you allow for bleed, or you will be a bit out).

Then, grab the centre (approximately) of the thing you want to centre, and drag it towards the guide, it will snap to the guide, perfectly centered.

Or you could just use the align palette. Make the background a layer and link it to the the layer you want to centre. Then click the appropriate button on the align palette.

Or you could just eyeball it, which I reckon gives the best results (if you've got a good eye).