OpenAds is pretty good if you want to set up something large scale. If not I have this handy little php script I wrote for one of my sites. You should be able to figure it out. I just left 2 entries to rotate.
file rotate.php
<?php
$item = array();
# array entries are url link, banner url, text
array_push($item,array("http://bbp.brazzers.com/m/mlib/109p/?t=34&nats=Mjg5NjE6MzoxOA,0,0,0,74871","bb/ava-lauren.jpg","Ava Laur
en"));
array_push($item,array("http://www.bigtitsroundasses.com/t1/cfree=howling/free_movies_bigtitsroundasses/btra2488.htm","bb/brandy
-talore.jpg","Brandy Talore"));
#display a random banner
srand ((double)microtime()*1000000);
$randomnum = rand(0, count($item)-1);
print "<table align=center><tr><td align=center><font size=2 face=tahoma><b>A Boob Girl Favorite</b></font></td></tr>\n";
print "<tr><td align=center><a target='_blank' href='" . $item[$randomnum][0] . "'>\n";
print "<img border=0 src='" . $item[$randomnum][1] . "'><br><font size=4><b>" . $item[$randomnum][2] . "</b></font></a></td></tr></table>\n";
?>
And inside my main php page I have
<? include('random.php');?>
where I want the random banner to show. Not fancy but does the trick.