Banners should be around 450x80... a bit bigger or smaller is fine. You can also put a short sentence about your site below the banner ("so-and-so specializes in great hosting", "insert some company phrase", etc.)
$20 through PayPal for two weeks (14 days). That'll give you a total of 70,000+ unique views to your banner or link.
I don't do rotating ads, only one ad for their paid time in the order I receive them... so your ad will be the only one on the page, never rotated out, and placed above the content on the frontpage, centered.... where the MvMMDI banner currently is (that's just a placeholder of sorts for another site I'm starting, the banner will be removed when the spot is sold).
I just finished two runs with www.engagedhost.com . I didn't ask how many hits / sales he received from his banner link, but after his initial two weeks were up, he immediately purchased a full month of banner space, so I suppose it worked out nicely for him.
Email: webmaster (at) musicmademe (dot) com
AIM: Kali Sweethog (going to bed soon, but I'll be online all day tomorrow)
ICQ: 16307319 (same deal as with AIM)
...or just reply here.
As of this typing, there is nobody waiting to have their banner up; so it's first come, first served.