With all of Amazon's wacky URLs, I never realized they added a simple mapping for browsing by tag:

http://www.amazon.com/tag/apple/
http://www.amazon.com/tag/microsoft

You can also subscribe to tags using:

http://www.amazon.com/rss/tag/apple/new
http://www.amazon.com/rss/tag/microsoft/new

There's even more hacking you can do with these URLs, like associates ids. Checkout the Amazon Web Services blog entry for more (Note: some of the URLs there are incorrect. Use 'tag' instead of 'tags' and '/new' seems required).

One thing Amazon hasn't made URL-simple is browsing for your own tags. Those still require the non-memorable http://www.amazon.com/gp/tagging/manage-tags/tag-name/ .