Professional Quality Photo enhancements?

I spend hundreds of dollars getting my daughters' pictures made at JC Penny's. One collage photo is 29.99. They offer the cd of all the unenhanced photo's with copyright release. I am very interested in buying a software that will allow me to make similar enhancements to my photos and I would love to make different collage pictures as well. What is the best software to buy that has collage formats and pro quality enhancement tools? It would be great to get to try the software free for a trail time.