Just google for “online banner maker” or “online banner generator”. You will find plenty of pages that can help you made banners. Most of them are free.
try http://www.bannersketch.com its a website that has a banner maker option where u can make your own banner in the site. no software download needed. i hope this helps.
Thanks for the suggestion KatieiR. Bannersketch is a great site as they are offering free way to create banners. However, i am more interested in making professional banners that may not be possible with bs. I am seeing good review on bannermall dot com, its bit costly (starting at $139) however they are making professional banners, let me give a try.