As others have said, it's not really clear what 'evolutionary distance' means

http://www.timetree.org/ will give you an estimate of the time since any two organisms last shared a common ancestor (as long as your organisms of interest are in the NCBI taxonomy, and someone has published a relevant study).

Using pubmed I found:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC540048/

DED: Database of Evolutionary Distances Nucleic Acids Res. 2005 January 1; 33(Database Issue): D442–D446. Published online 2004 December 17. doi: 10.1093/nar/gki094.

There's an iPhone app for that :)

I think www.timetree.org is a great site, if by evolutionary distance you mean divergence time. If you like a non-molecular approach to dating this paper is a good summary of fossil-derived dates between animal groups (Benton and Donoghue 2007 10.1093/molbev/msl150).

Using a number calculated from sequences (e.g. 9.5% different), the approach used by DED in Pierre's answer, is OK but not as good as using a patristic distance. That is essentially the path distance between two taxa on a tree. If you have a reliable tree for the organisms you can get the patristic distance using Bio::Phylo calc_patristic_distance(), or see the java application PATRISTIC.