A website called "Name Thesaurus" will give you variations of both surnames and forenames. It is easy to use and gives some surprising results.
On the home page you are given a form in which to enter either a surname or a forename (given name), and it is as simple as that. The results page will then list matches that are variations of the entered name, soundex matches, and metaphone matches. If you ever wonder exactly what the soundex and metaphone choices in search engines (such as Ancestry and FamilySearch) look for, now you know. And if you want to manually enter some spelling variations yourself, this site will give you plenty of options.
I entered the surname summers and got 280 spelling variations, 4090 soundex matches, and 366 metaphone matches.
Thanks to Debbe Hagner for this site suggestion. Debbe was the speaker at the November GPS meeting where she talked about breaking down brick walls. This site is one she recommends to help do that.
You can explore the site at http://www.namethesaurus.com/Thesaurus/