I just mentioned this on another lag thread, but this app has helped fix any lag:
It works great and always gives me a boost. You do need to be rooted to use it since it trims the cache on the processor. Android trims its own cache fairly well, but it doesn't automatically trim the processor so this app helps keep my phone running smoothly. I don't have to use it more than once a day at most, usually it's more like every other day or even a couple of times a week.