The Sunday Comics Time Tunnel is an easy way to view the Sunday comics online. I've updated it with the Chronicle's current Sunday lineup and have added comics from Yahoo and elsewhere.
Let me know if there are any other Sunday comics you'd like me to add or if you have any problems with links working.
For daily non-Sunday comics, I recommend the Chronicle daily comics page. And if you're interested in reading the soap strips from years gone by, check out the Comic Archives Navigator.