How to include html tags within a wordpress excerpt?
As I see it, you can only use method 2 and 3; both of them can be updated via WordPress' back-end with virtually no programming required which is ideal if you're going to be installing and using them on client sites.
Here's a tutorial with working code for method 3 -- http://aaronrussell.co.uk/legacy/improving-wordpress-the_excerpt/ and here's a plugin to use method 2 -- http://wordpress.org/extend/plugins/advanced-excerpt/