Seems like every state has a giant music festival near the end of summer, and Arizona won't be left out of that! Just barely staying in the summer season, from September 26-28th at Tempe Beach Park residents and travelers alike go to Summers End Music Festival for both old and new music. Featuring alternative and rock music, bands like "Capital Cities" and "American Authors" are playing friday, "The Replacements" and "Taking Back Sunday" on Saturday, and "Foster The People" due to kill it on Sunday. "Fitz & the Tantrums" are also on Sunday, and they perform 110% so if you're going to be at Summers End be sure to check them out. Bonus: since the festival isn't until late September, the weather won't be too blistering.
Find out all the festival info here: http://www.summerendsmusicfestival.info/band-lineup