Gallup Daily: Tracking Election 2008
Based on polling conducted Feb. 23-25, 2008
[...] John McCain's support as the GOP nominee among Republican voters continues to be roughly triple that of his closest challenger, Mike Huckabee. The latest Gallup Poll Daily tracking figures show McCain to be the choice of 64% of Republicans and Huckabee the preferred nominee of 20%. That level of Huckabee support matches his lowest since Mitt Romney exited the race. Huckabee's support rose as high as 29% after Romney suspended his campaign. -- Jeff Jones
You can follow the above link for a current graph and data on the Democrat race as well.
Democrats, Republicans: Obama Likely to Win Nomination