The common alignements are right, left, centered and justified. The items shouldn't fly around but should be connected through visual lines. If possible there should be an hard edge for the eye to follow, so it's easier for the reader to read the text.

In webdesign it is best to stick with a single alignment or complimentary alignments. Lines can be created for the eyes by alignments of the text. Alignment holds the contents of the page together and creates unity and harmony.

Forms: By designing  a form site, alignment of text outside the form area is very important. So the use of a complimentary alignment creates a stong edge for the eyes to follow by reading the text.

Navigation: navigation should be of interest for the reader, so he wants to click on and surf around. So the alignement can improve the the navigation elements Try to avoid thick borders on tables. On a horizontal navigation bar it is good use to place the links the "valign=top" attribute.
On a vertical navigation bar it is good use to align the links left or right side.

I found this website and thought this is a good example for well done allignement. The picture on the left top side has some slanting lines leading to the top of the page. The links are the connection between the slanting lines, but also have the hard edge on the right side to connect to the text on the right side. The empty space around is set up very clean. I like the fading effect of the left top image as also the colors which are set up very light but good readable.