Unless you're referring to something else, I use the "market scanner" page available from Interactive Brokers for this. I like screening for "Top % Gainers" every day for targets of opportunity.
I filter for US stocks > $1 and < $100 and > 50,000 avg volume.
For instance, as of this writing (about 0815 NY time) I see that SNDK, ORCL, NVDA, LEND and CMGI are all posting significant gains pre-market (3% plus) These could provide interesting fun for today.
Is it the most effective? I don't know. But it's the one I use.
Trader Mike (tradermike.net) does similar screens every morning, though I'm not sure what tools he uses to do this.