There are thousands out there, and some really great ones.
One I subscribe to and get daily posts from is Katherine Tyrell's Making a Mark.
Katherine is a talented artist, working mostly in colour pencils and pastels and she writes about and comments on almost everything imaginable relating to drawing and art. This is one of the most informative and diverse art related website/blogsites I've come across so far and its also bursting with links to other great blogs.
Katherine also writes some wonderful blogs, 'Travels with a Sketchbook' http://travelsketch.blogspot.com/ being one of a few, in which she posts and talks about her sketches. Well worth seeing. She even provides valuable information about setting up your own Art Blog.
From her site I've also come across - Urban Sketchers http://www.urbansketchers.com/ which is a diverse group of sketchers worldwide and most definitely worth looking at, as are all the blogs she has linked to.
Probably my favourite blogsite at the moment is by a Sydney architect (and her little bear!):
Liz & Borromini http://www.lizsteel.com/
Liz also seems to sketch constantly and has been travelling frequently to all sorts of wonderful places, but when she's in Sydney she seems to spend a lot of time sitting in a cafe or tearooms sampling their tea and doing the most beautiful loose brightly coloured sketches! For those Sydneysiders reading this, you will recognise many of the cafes she's sketching in. Oh to be able to draw like that!
'Well these are just a few for starters, but make the time to check them out for yourself - and be prepared to disappear into a world of wonderful visuals and insightful reading! Any comments or suggestions of other Art Blogs will be gratefully received!