oneFN

To quote oneFN's website:

"OneFN has the largest reach among active, high net worth online investors, who are also affluent consumers. OneFN provides sales and marketing strategy services for its network of quality financial publishers including outsourced solutions for advertising sales, list management, and direct response sales of financial and demographically aligning products."

...In other words, if you're a branded site hawking financial advice to rich people, this would be the place to go. Multiple banner sizes and formats, including pop-up and pop-under.

Network features:

Over 5,000,000+ unique users
Currently 22+ affiliated financial publishers including Thomson Financial, Stockpoint and Zacks and the Motley Fool.
400 million+ ad impressions available monthly
2MM+ opt-in records for list rental marketing

No stated traffic minimum, but based on the network profile one would assume at least 500,000 monthly impressions.

UPDATE

Website is no longer online.