If you can brave the old Chinese ladies (seriously, much tougher than they look), there's a booth at the corner of 8th and Washington where they sell their daily "off" catch. The lady tells me everything was caught earlier that morning. EVERYTHING I have purchased there is amazingly fresh, (i.e. still in rigor, the "really fresh fish slime", red gills, bright, shimmery, metallic skin)
Warning: these are whole fish, not cleaned (they don't clean for you), so there is a fair amount of labor associated with purchase.
The selection varies based on the season, but last week they had
Sardines ($3/lb or $5/3lb)
In the past I've also seen:
Black cod heads ($1.5/lb)
Funny, if you ask her how to cook certain fish I guarantee she'll say "fry it" or "make soup" every single time.