First of all, I think everyone should be checking out Mosaic Geek's work: http://www.mosaicgeek.com/
Shannon Kuchera, the artist behind Mosaic Geek is an amazing person who totally inspired me to go and learn about mosaics and who I aspire to be as good as. Her mosaics are often based on retro video games which I just think is inspired and brilliant and she has recently been making mini-mosaics too. On the basis that I find it hard to cut a fairly big piece of glass into a smaller bit, my admiration is extreme. Check out her site now. And then go straight to Etsy and order one of those cute pacman mosaics or a tetris necklace.
Other than being totally awesome, Mosaic Geek are also pretty good at introducing other mosaic artists. I don't know much about these two artists (I need to do some research!) but to see some truly amazing mosaics have a look at these:
http://www.mosaicsphere.com/gallery.html - wow. Planetary mosaics. Amazing.
http://www.flickr.com/photos/laura_in_spain/4563045108/in/faves-mosaicgeek/ This photo made my jaw drop. It is astounding and I absolutely love it. Colours, textures, materials... I could look at it for hours.
I'm sure there are lots of others that have been recommended, but at the moment I can't remember them. I shall start updating when I find new inspiring pieces.