Programs and editors/MCPatcher
MCPatcher is a tool that allows you to install mods into minecraft, create backups and add full support for HD and semi-HD texturepacks.
More information, details and downloads can be found at the forum thread here.
MCPatcher is a very easy sort of mod downloader.
To use it, open MCPatcher then click the '+' button. This will open up your browser. To load a mod, choose the mod you would like to install, then click 'OK.' The mod formatting box will show what is inside the mod. When this pops up click 'OK.'
When you have your mods in, click 'Patch' to install them. There are also mods already pre-added on MCPatcher, like HD Texture Support and CTM. Hover your mouse over them so you can learn what they do.