google for weka dataset  example  

Check this website 

http://www.rdatamining.com/

This is the famous one "UCI Machine Learning Repository":

https://archive.ics.uci.edu/ml/datasets.html

https://archive.ics.uci.edu/ml/datasets.html

http://asrs.arc.nasa.gov/search/database.html

ASRS Database Online 

UCI MACHINE LEARNING REPOSITORY ; OASIS Data Set (http://www.cms.gov/Medicare); fundas image data sets

Thanks Mr. Mohamed Mahmoud Hafez...this link is very useful for me..

Thanks Mr. Ahmad and Abhay Kumar.....

If you are performing data analysis using R, you will find many dataset packages in R that you can install and use.

For example:

http://www.inside-r.org/packages/cran/psy/docs/ehd 

• If you talk about online..
• Take any source page of web site, it will be in html or xml form. Retrieve data using XSLT and getElementById then store in a database. Now online database is ready for use and the operations performed are also on real tme data.
• if you talk about existing database
• You can use either Weka tool or R Graphs.

In Weka tool you can use existing database or you can upload your own database and analyze it as per your requirements.

If you use R graphs, you can use or uploaded database of your own, derive statistical methods for querying, now you can analyze data after each andank every equation derived.

Both are free to download. Weka tool has got some limitations, you can go with other dataming tools after having acquaintance with Weka,Clementile ...

Thanks

Thanks Ms Rekha for useful link...

Thanks Lalitha....