Have you ever seen an advertisements sliding upwards only after the page loads for few seconds? I have personally seen this on Sitepoint and I think it is good way of getting exposure at at the same time not as annoying as popup because it still does not disturb the page you are viewing.
This cool little script, catfish is actually made by Ian Purton, and it uses iframe to implement the advertisements sliding from the bottom. There is few command which you could after the way you want your advertisements to appear, including sliding time, delay, url, height and increment per millisecond.
I am still having trouble embeding this onto my blog because it seems that there is error on IE7 only on WordPress. This script would run normally onto a html. I think there is something that could not run concurrently with wordpress.
If you are interested to implement this onto your websites.