We've actually got a thread where various members have submitted banners that they have made for the forum:
http://forum.jphip.com/index.php?topic=12042.0Certain banners have been set to primarily show up in certain sections of the forum (e.g. AKB-themed banners can usually be seen in the AKBar, SNSD/KPop ones are primarily seen in the House of Seoul, and "adult" banners are geared for the RLD) while others show up everywhere.
That thread is currently 20 pages, so based on that, the total number of banners here has easily got to be at least up in the 3 digit (i.e. hundreds) range, if not more.