Over at Pollster.com, they do an excellent job of keeping track of pretty much every national poll thats out there - and analysing 'em.
One thing that they'll warn against time and time again is not to read too much in any one single poll. Margins of error and the like mean that any one poll can swerve up and down quite markedly without statistical significance, and differences between pollsters mean that on top of that, there can be conspicuous differences between the results of different pollsters - and then you have the occasional outlier.
So what they strongly suggest is to look at the average of the last X polls out. They track exactly that, charting out a very cautious trend estimate.
In this image, the lines represent the trend estimate; whereas every individual dot represents one poll result. (And just look at how large the variation from one individual poll to another is..)
As you can see, Giuliani, who surged in the winter months, has been steadily dropping since - and below him, McCain has been dropping at roughly the same rate.
Romney has been creeping up to ten percent, passing Gingrich, who seems to have lost any momentum he may have had. But the big story is Fred Thompson, who's surged up to where he's almost past McCain.
Note that the graph was last updated three days ago.