There's the Perry Bible Fellowship
which appears in the Guardian from time to time (which is strange seeing as it isn't usually that family friendly). Probably one of my favourite comics ever though.
Sometimes it takes a few read throughs to get, but it's worth it (it's best to start from the older ones first).
I've read Fred Basset a few times and it is definitely one of the most unfunny comics I've read (almost rivalling Garfield and Ctrl+Alt+Del).
I read some of the Dilbert strips online quite a bit, they're usually good for a laugh, but I've not seen them appear in any newspapers over here though, just on calendars on compilation books.
It's sad that most webcomics trash most of the stuff that appears in newspapers.
Also, it'd be great to have Sam and Max appear in newspapers, but they probably wouldn't fit in with the small 3 panel layouts newspapers all seem to want and still keep everything I like about the longer comics.