pc slow down

anyone recomend a spyware remover program.my pc seems to be running very slow & i have run an av program which comes up clear now . preferably with a link as when you search for these things it allways seems to take you where your likely to pick up more problems than what your trying to fix. in the past i have used various programs but would like some input as to what has worked best for you.

pc in running a legit vista operating system & fully updated with avast as the av program