First step I would recommend is kill your antivirus. From my experience, wide spread OS X viruses are not common. Unless you have Snow Leopard, or you have actually had an experience with an OS X virus, just get rid of antivirus. It just slows things down by constantly scanning.
Second: if you deleted big apps, make sure you also emptied your trash. Unless you emptied your trash, trashed files stay on your hard disk, using space.
Third: Empty your caches. You can do this with a program called Onyx.http://www.macupdate.com/app/mac/11582/onyx
Fourth: If you have done all of the above and your machine is still abnormally slow, verify disk permisions. Sometimes, disk permisions can become damaged or altered, causing mac to have to work harder at accessing a particular file.
The beach ball just keeps on spinning. I've run all the virus software, disk warrior, deleted big apps, changed start up apps and still runs slow. Any ideas?
Are you talking in general or while on the internet in regards running slow. Mine was running very slow on the internet and the way I fixed it was to DELETE my home wifi in Preferences/Network/Advanced, then reboot. After the MBA started back up, I reconnected to my home network and the difference was night/day and the computer has been "popping" ever since.