You don't have to have the latest and greatest photo editing software to get access to some good basic photo fix routines. After cropping, and straightening, improving lighting is probably the most desirable fix. However this is often a multi-step process.
This is a one step automatic automatic lighting correction called DxO lighting is available as a net based fix from the Fd's flickr toys site (which has a lot of other fun photo manipulation toys). Even if you don't have a flickr accont you can use this site, but it is flickr oriented. If you like the results and want to look at the commercial package check out the DxO site.