You should note that the canvas tag is a part of HTML5, and as such is only supported by Mozilla Firefox, Google Chrome and Apple Safari. Opera supports a small amount of HTML5, but it does not support the canvas text and shadow APIs. However Microsoft Internet Explorer does not yet support it (up to 8), and support is being given in IE9, therefore it is advisable not use HTML5 in mainstream use.
Harmony is a drawing tool that uses the whole page for the canvas. It has 11 different "brushes" you can use and you make some rather interesting shapes/images with the tool. It takes a while to get used to the tools and how they interact interact with each other, as when the lines cross over or come close they create different types of effects.
Tile Track was created by Julian Rosenblum, no information is given on the game or instructions. Tile Track is a very addictive game where you use the cursor keys to guide the smiley face getting rid of all the green squares before you get to the final red square. Although the first two levels are very simple, the next ones may require a few turns to complete.
Cubeout is a remake of Blockout (a 3D Tetris game) in HTML5. It works in Firefox, Chrome, Opera and Safari though it is best when using Chrome and Opera. It has all the features you would expect in Tetris including being able to rotate the blocks (in a 3 dimensional way), move the blocks and to accelerate their fall. You can also step away from your high score game by pausing it.
EtchaPhysics is a cross-browser, gesture-enabled physics game for the HTML5 Canvas. It has Classic Etcha-Sketch functions like "Shake to Clear" and "Dial To Draw" coupled with a touch and gesture-enabled drawing interface create an addictive and fun environment. There are 15 addicting levels and 10 unique game-modes, and it is also iPod Touch / iPhone compatible.
"Same Game" is an addictive game where you have to remove all the circles by clicking on them. You can only remove circles where there are two of the same colour next to each other. You also have options to change the number of colours and the grid size shown.
UFO is in its second version and is a rather fast paced game. You control a UFO and press space bar to fire at tanks, which in turn also fire towards you. It is a similar game to space invaders, but in reverse, you are in the air, and they are on the floor.
3bored is an addictive game where you have to avoid gun fire coming from tanks and planes (and as you progress, depth charges and orbital laser strikes.) It's rather hard to get used to it at first with a fast paced action, but after playing it a few times it becomes very addictive.
Ben Joffe experimented with using textures with Canvas. He has created what at first, looks like you're about to play Doom. Unfortunately you cannot shoot your gun, but is it very smooth even with a high resolution on the textures.
This is an experiment where you can interact with the mouse. Moving the mouse around will make the particles follow it, clicking will make them rush out and come back, whereas holding down the mouse button will make them stay away from your mouse.
Addy has created a 3D Google gift box. You can use the mouse to rotate the box. Typing in your search query and clicking Search will open the box up to reveal your search results.
An experiment where it uses both the canvas and the audio tag. The circles on the page move and flash in conjunction with the audio.
Below are some links for further reading on the canvas tag, including information about it and tutorials on using the canvas tag.
Wikipedia: HTML5 Canvas
The Canvas Element
Mozillas Canvas Tutorial
Diving Into Canvas
Operas Cavans Painting