Actually no program can guarantee you 80-90% comperssion ratio. It all depends on the files you are compressing. Text files(*.txt), MsWord document files, etc. can be compressed a lot while JPEG files, GIF files and other popular non vector graphics files wont be compressed to a great extent. You must have noticed that in many games(also in Digit's CD's/DVD's) which are distributed in ZIP or RAR formats have a good amount of comperssion ratio. Its because they have a lot of information in ASCII(text, code, symbols, etc.) in many files they contain and the fact that there are a lot of files in them and a minimum of MPG, JPEG, GIF, etc. files.
While the best program I know about is WinRAR, 7-Zip is also good.
I hope this info has been useful to you.
Here are some EXTREMELY USEFUL links for your furthur information:
(Usefullness in their respective order)
1. *en.wikipedia.org/wiki/Data_compression
2. *en.wikipedia.org/wiki/Image:Compression_ratio.svg
3. *answers.google.com/answers/threadview?id=749492
4. *www.maximumcompression.com/data/summary_mf.php
5. *www.chin.gc.ca/English/Digital_Content/Capture_Collections/Sub_sections/fnd_file_compression.html
6. *www.google.com/search?hl=en&client...result&cd=1&q=file+compression+ratios&spell=1
