Otto Timmons told us this about the banner ad above, which was one of the first banner ads ever and ran on Hotwired in 1994.
Although we had the most popular ad on Hotwired (according to Brian and Matt...) there were at least five or six other banner ads that launched at the same time and they too should get credit for being "first". I can remember Club Med, AT&T, ZIMA. Last but not least, O'Reilly's Global Network Navigator, GNN, started accepting paid advertising at the same time (one banner ad on the home page, as I recall)
These days online advertising has gotten sneakier, as the consumer has forever been in an arms race against spam and banners ads, with filters, whitelists and adblocks. Not to mention, astroturfers.