I have heard stories of Japanese World War II veterans who hid out in
caves or jungles for years, thinking the war was still going on and
even occasionally shooting people.  One story was of a Japanese
soldier in either Indonesia, Malaysia or the Philippines (I think it
was the Philippines) who stayed in the Jungle for 30 years, shooting
farmers whenever he had the chance.  I saw that one on the history
channel.  I would like any web-based information on this type of
phenomenon.

Dear danath,

Here are, as a result of my research, the three best web-based sources
I found containing information on the phenomenon of Japanese soldiers
who refused to surrender and continued to fight, believing that the
war was not over.

--

This comprehensive website is dedicated especially to the numerous
examples of Japanese soldiers who did not surrender for years or even
decades after the war was over, the so-called "Holdouts":

No Surrender: Japanese Holdouts after WWII, by Justin Taylan
http://www.wanpela.com/holdouts/

--

Here is a website telling the full story of the particular soldier you
mentioned who stayed in the jungle of the Philippines for 30 years:

Wake Forest University: Hiroo Onoda - Thirty Years in the Jungle, by
Jennifer Bernet
http://www.wfu.edu/users/bernjd1/asia-pacific/index.html

--

This website is about Shoichi Yokoi, the last Japanese WWII straggler
on Guam, who was discovered in 1972 after 28 years:

The Ultimate Guide to Guam: Shoichi Yokoi - Last Japanese WWII
Straggler on Guam
http://ns.gov.gu/scrollapplet/sergeant.html

--

As far as I could find out, the last Japanese WWII soldier who
surrendered was Captain Fumio Nakahira who held out until April, 1980,
before being discovered at Mt. Halcon, Mindoro Island, in the
Philippines. He is mentioned here:

George Duncan's Lesser Known Facts Of World War II
http://members.iinet.net.au/~gduncan/Facts-2.html

--

I really wish I had found even more detailed documentations on this
fascinating topic; but as it seems, not much research has yet been
done on this highly interesting phenomenon.

Sources:

Darby Rangers: Battle for Okinawa - The Perfect Pillbox
http://darbysrangers.tripod.com/Okinawa/id8.htm

Illinois State University: Fighting to the Bitter End - The Japanese
Army in the Pacific Theater 1945
http://www.history.ilstu.edu/education/learnteachamerhist/pacifictheaterinfo.htm


Search terms used:
"last japanese soldiers"
://www.google.de/search?q=%22last+japanese+soldiers%22&hl=de&lr=&ie=UTF-8&oe=UTF-8&newwindow=1&start=10&sa=N
"Hiroo Onoda"
://www.google.de/search?q=%22Hiroo+Onoda%22&ie=UTF-8&oe=UTF-8&hl=de&btnG=Google+Suche&meta=
"Hiroo Onoda" "Shoichi Yokoi"
://www.google.de/search?q=%22Hiroo+Onoda%22+%22Shoichi+Yokoi%22&hl=de&lr=&ie=UTF-8&oe=UTF-8&newwindow=1&start=20&sa=N
"Fumio Nakahira"
://www.google.de/search?q=%22Fumio+Nakahira%22&hl=de&lr=&ie=UTF-8&oe=UTF-8&newwindow=1&start=0&sa=N
"Japanese stragglers" 1974
://www.google.de/search?hl=de&ie=UTF-8&oe=UTF-8&newwindow=1&q=%22Japanese+stragglers%22+1974&meta=
"Japanese stragglers"
://www.google.de/search?hl=de&ie=UTF-8&oe=UTF-8&newwindow=1&q=%22Japanese+stragglers%22&btnG=Google+Suche&meta=
"Japanese Holdouts" 1972
://www.google.de/search?hl=de&ie=UTF-8&oe=UTF-8&newwindow=1&q=%22Japanese+Holdouts%22+1972&meta=
"Japanese 'Holdouts"
://www.google.de/search?q=%22Japanese+%27Holdouts%22&ie=UTF-8&oe=UTF-8&hl=de&meta=

Hope this proves useful!
Best regards,
Scriptor

Excellent response, thank you very much.