A place called comics.com ought to be a good place to see comics - and it is.
ComicsPage.com has an archive of around six months, but the interface is not as friendly.
If you're looking for Mr. Boffo or Cats with Hands, they no longer appear at ComicsPage.com. They are now found at the Mr. Boffo web site.
King Features has changed their web site so that they no longer offer every date of the comics they syndicate. Fortunately, it appears that all of the comics I am interested in are available on the Seattle Post-Intelligencer web site.
Gocomics.com (previously named Ucomics.com) has comics, but only the last month of mainstream comics are free.
If you're looking for Lost Sheep, it now appears at the Humorous Maximus web site.
Barkeater Lake is no longer available at comics.com. It now has it's own site.
The Bob the Squirrel comic site.
The Buckles comic site.
The Doonesbury comic site (hosted at Slate).
The Farcus comic site (only two weeks are available).
The Garfield comic site.
Editorial cartoons by J. D. Crowe.
The Little Dee comic site.
The Pluggers comic site (they only have a three month archive here, as opposed to the six month archive at ComicsPage.com). If you like this you may also like his editorial cartoons.
The Rhymes With Orange comic site.
Sheldon is no longer available at comics.com. It now has it's own site.
Here is the Among Wolves comic site (in case you don't want to visit Comics Sherpa at Gocomics.com.
Here is the Keenspot site.