Hi Lindsay,
Generally relative urls are best both for links and for redirects, however if for some reason you really need to get a fully qualified url, you can pass the relative url into one of our utility methods.
using mojoPortal.Web.Framework;
string relativeUrl = "/foo.aspx";
bool forceHttps = false;
string fullUrl = WebUtils.ResolveServerUrl(relativeUrl, forceHttps);
If you pass in an url that is already fully qualified it just returns the url you passed in so it is safe to use this method even if you are unsure of whether you are passing in a relative url or not.
Note that SiteUtils.GetCurrentPageUrl() is designed only for CMS pages, ie the pages that make up the main menu. Its primary use is for returning to the cms page from a feature supporting page or edit page in features that have supporting pages like the blog, forums etc.
Hope that helps,
Joe