First of all you need to learn to write. Especially since you are a freelance writer. There is no plugin for that, unfortunately.
My plugins are:
xml sitemaps
akismet
wp cache (not super cache, that one sucks)
nextgen gallery
all in one seo pack
cforms II
digg digg
fd feedburner plugin
easy gravatars (people like web 2.0 cutesy bullshit)
sociable
sphinn it
and of course the almighty motherfucking pingcrawl.
EDIT: Actually, sorry aequitas, but I don't agree to that plugin list. It sure is helpful to newbies though.