sh404sef 188.8.131.521, is the most popular joomla url sef / search engine friendly extension. It is also titled as the 'editors pick extension' in the joomla extension directory. Also the plain interface and easy usability help you website's seo.
If you have events that people must pay to register to attend ? DT Register is the answer. With DT Register you can configure the event registration online where you can get the information of the applicants and payments via credit card.