When I work on pixel art, I use MS Paint and Paint Shop Pro 11. It works fine for me making simple game graphics, though I'm sure professionals would prefer something else.
When making pixel art (primarily tiles), I need to view the image tiled side by side to see if it's seamless or not. If I'm currently working in MS Paint and don't have Paint Shop Pro 11 open, I need to:
[font=courier new,courier,monospace]Open Paint Shop Pro -> wait for it to load -> Paste the image in -> (And in the menu:) "Effects -> Image Effects -> Seamless tiling..." -> Check 'Show preview' -> In the preview window, check 'Show original'[/font]
Not cool. So I made a tool that I made that lets you right-click on a image file in Windows Explorer, and select "View image tiled", and wallah!
Note: This does not change any file ascosiations; your files will open using the same preffered default program they always do. All it does is add a single simple 'View image tiled' context menu command, and only on the file extensions you select (Supports: PNG, Gif, Jpg, BMP, and Tiff). You don't even have to enable the context menu integration at all, if you don't want to. You can just open the tool and drag-and-drop or copy-and-paste your images in for viewing.
download itfor free from GD.net's marketplace (Windows only). If you find it useful, donate $5 and buy me a pizza*.
*[size=2]Warning: Money will not actually be spent on pizza. Chances are that it'll go to further my raw cookie-dough or Dr Pepper addictions, or perhaps blown on a indie game.