Your approach to investing has to change if you think you can time the market. I just read an article at yahoo finance which backs up what I've known for years, that timing the market is virtually impossible.
1983-2003 period for S&P 500
Buy and Hold ~ 10%
Minus 30 worst days ~ 19%
Minus 20 best days ~ 5%
Moral of the story is that if you are willing to risk missing the best days trying to miss the worst days, go ahead but you will have probably wasted a lot of your time, and money and got nowhere. You need to change your approach to investing.
I have said it before and will say it again, buy a no-load mutual fund or ETF that tracks the S&P 500 and you are doing really all you can do.