Best way to delete files

If I want to delete a file that cant be retrieved with a recovery whats the best way?
Answer #1
Look here…
http://www.pcworld.com/article/2155347/how-to-guarantee-your-data-is-truly-deleted-before-recycling-old-pcs-and-drives.html
This is good also…
http://download.cnet.com/Eraser/3000-2092_4-10231814.html
Answer #2
eraser is will kill files without chance of getting them back.
Answer #3
if you are asking for a single file , any file shredder would do the job. if you are asking for whole harddrive , you need to make overwrite on it with an options like 1 pass ,3 pass , 7 pass and such. argument over which pass totally secures every file , is really headache. for me if you are not handing over your harddrive to a maniac which would dig its deepest layers , even 1 pass would be enough. also many more overwrites will be done as that person uses that harddrive.
there are many 3rd party software for overwrite but the famous software ccleaner has also that option , you can use it , since no matter which software you use , pass algorithms will be same .