I want to ad more ad to the 400x60 ad space which got empty after google canceled their referral program. I cannot add more adsense there as i already have finished up the limit of 3 ad units in a page. Can you suggest me any other programs which i can fill that space with?
There's nothing wrong with monetizing your blog by selling ad space. Just look at popular blogs like Problogger or DoshDosh and you'll see ads along the right side of their pages and links that say "advertise here".
Google frowns upon selling text links for PageRank purposes. Personally I don't see why they should dictate how a blogger chooses to monetize their site, but that's their stance.
This comment is not about which program to promote, but if I have odd sizes (Which seldom happens as I buy templates or pay for a design), I'll create my own banners or text ads then link out to the program with a standard html link.
Like what quest mentioned, you can create your own
banner. Or you can use banners from affiliate programs
like in ClickBank. When you made a sale, you will
earn the commission instead of earning from selling
the banner space.