Gopi,
I have not managed or run performance tests myself to give you and answer, but I will throw in my two cents which may help get you going -or- may guide you to list some additional info which will help someone else give you a better reply.
What research have you done on Google so far? I Googled "performance test web services" and found a number of sites including this
opensource tools site. You may want to look through these and see if any of them meet your needs.
If that does not help, then you may want to describe a little deeper what you are trying to test in terms of number of concurrent users, transactions per second, response time requirements and so forth. Depending on what your performance goals/requirements are in general may help folks scope their replies to you. It may also help to know if you have any budget limitations (or better worded, what your budget limitations are).
I believe some tools such as LoadRunner will run you a minimum of tens of thousands of dollars (like $50,000+) when you by the minimum licenses and support agreements - no point in being led down that path if your budget is $100 ;)
Good luck!