That photoshop trick...

umm.. Can't you go image>rotate or something like that?

That sorta works, but this had to do with drawing a line and rotating the picture to it.

Skew perhaps?

There are a couple ways to do it. The easiest is to use the crop tool(c). Drag open a crop-> move your cursor outside the box-> L click and hold-> move the cursor to match the crop line with what is straight in the image-> drag corners to maximize image size-> double click inside the crop area.

If it's a distortion thing you can use the skew tool. Select all(ctrl A)-> edit>transform>skew->use the corners to adjust->double click inside. It helps a lot to use the grid(ctrl ') to make sure it is perfect.

you can also do it in picasa.

with drawing a line? ok heres how i think it would work:

load the picture in ps, then hold shift while you draw a pencil line across on a new layer. you can move the pencil line to something that you want to be level in the picture. now you can rotate the image (make sure that if the image is the background layer, you duplicate it and delete the background layer so it is not locked). there will be some corners showing. so just crop it out. the way i crop is i use the rectangular marquee and draw my box to the part of the image i want to keep then go image>crop