What are some alternatives?
When comparing XML-Sitemaps.com and A1 Sitemap Generator, you can also consider the following products
DYNO Mapper - Create Sitemaps with the DYNO Mapper Visual Sitemap Generator.
Screaming Frog SEO Spider - The Screaming Frog SEO Spider is a small desktop program (PC or Mac) which crawls websites’ links...
WonderWebWare Sitemap Generator - Sitemap Generator is freeware program that will help you to automatically generate site maps for google, bing and yahoo in their respective file formats.
GlooMaps - Create your visual sitemap on the go - easy peasy
FlowMapp - UX planning tool for creating a visual sitemap
SEO Crawler - A web-based crawler with real-time crawl feedback.