The Content Extract plugin providing more control over excerpts has been updated to fix a bug that was preventing html being stripped out of excerpts. Since html stripping should be the default behaviour this was a silly bug badly in need of a fix.
Anyway, if you seek more advanced control over your excerpts, or want to have them auto-generated from your main body content and written into the database, or have them contain html codes, trigger them at a variable length and a range of other options, the Content Extract plugin might be what you seek.
Full details and/or download the zip archive from Webspace Works.
n.b. Please note that this link is different from that previously posted here, following reorganisation of the site.