So, for starters, here are a few. Please note that you need to register at some of these sites to gain access to the online copies:
General Science
 | Nature
| Science
| New Scientist
| Scientific American
| |
Chemistry
list of journals published by the American Chemical SocietyA list of journals published by the Royal Society of Chemistry
An exhaustive list of journals (with more than 600 entries) as published by ChemConnect
Want to see of some of your favourite journals before they appear? Try Elsevier's