Custom bullet symbol for <li> elements in <ul> that is a regular character, and not an image

This is a late answer, but I just came across this... To get the indenting correct on any lines that wrap, try it this way:

ul {
  list-style: none;
  margin-left: 0;
  padding-left: 0;
}

li {
  padding-left: 1em;
  text-indent: -1em;
}

li:before {
  content: "+";
  padding-right: 5px;
}

The following is quoted from Taming Lists:

There may be times when you have a list, but you don’t want any bullets, or you want to use some other character in place of the bullet. Again, CSS provides a straightforward solution. Simply add list-style: none; to your rule and force the LIs to display with hanging indents. The rule will look something like this:

ul {
   list-style: none;
   margin-left: 0;
   padding-left: 1em;
   text-indent: -1em;
}

Either the padding or the margin needs to be set to zero, with the other one set to 1em. Depending on the “bullet” that you choose, you may need to modify this value. The negative text-indent causes the first line to be moved to the left by that amount, creating a hanging indent.

The HTML will contain our standard UL, but with whatever character or HTML entity that you want to use in place of the bullet preceding the content of the list item. In our case we'll be using », the right double angle quote: ».

» Item 1
» Item 2
» Item 3
» Item 4
» Item 5 we'll make
   a bit longer so that
   it will wrap

So many solutions.
But I still think there is room for improvement.

Advantages:

• very compact code
• works with any font size
  (no absolute pixel values contained)
• aligns rows perfectly
  (no slight shift between first line and following lines)

ul {
	position: relative;
	list-style: none;
	margin-left: 0;
	padding-left: 1.2em;
}
ul li:before {
	content: "+";
	position: absolute;
	left: 0;
}

<ul>
  <li>Curabitur non nulla sit amet nisl tempus convallis quis ac lectus. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Donec velit neque, auctor sit amet aliquam vel, ullamcorper sit amet ligula. Pellentesque in ipsum id orci porta dapibus.</li>
  <li>Nulla porttitor accumsan tincidunt. Mauris blandit aliquet elit, eget tincidunt nibh pulvinar a. Aliquet quam id dui posuere blandit. Curabitur non nulla sit amet nisl tempus convallis quis ac lectus.</li>
</ul>