Key commands to quickly create Markdown headers in Brett Terpstra's MarkdownEditing plugin for Sublime Text 2. ⌘^1 for #, ⌘^2 for ## and so on. Works on selected text too. Just add the following anywhere in your Default (OSX).sublime-keymap file for MarkdownEditing (or any relevant package for ST2)

gistfile1.json

    { "keys": ["super+ctrl+1"], "command": "insert_snippet", "args": {"contents": "# $0"}, "context":
     [
         { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
         { "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
         { "key": "following_text", "operator": "regex_contains", "operand": "^(?:\t| |\\)|]|\\}|$)", "match_all": true },
         { "key": "preceding_text", "operator": "not_regex_contains", "operand": "['a-zA-Z0-9_]$", "match_all": true },
         { "key": "eol_selector", "operator": "not_equal", "operand": "string.quoted.single", "match_all": true },
         { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
     ]
    },
    { "keys": ["super+ctrl+1"], "command": "insert_snippet", "args": {"contents": "#${0: ${SELECTION/(^ | $)//g} }#\n\n$1"}, "context":
        [
            { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
            { "key": "selection_empty", "operator": "equal", "operand": false, "match_all": true },
            { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
        ]
    },
    { "keys": ["super+ctrl+2"], "command": "insert_snippet", "args": {"contents": "## $0"}, "context":
     [
         { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
         { "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
         { "key": "following_text", "operator": "regex_contains", "operand": "^(?:\t| |\\)|]|\\}|$)", "match_all": true },
         { "key": "preceding_text", "operator": "not_regex_contains", "operand": "['a-zA-Z0-9_]$", "match_all": true },
         { "key": "eol_selector", "operator": "not_equal", "operand": "string.quoted.single", "match_all": true },
         { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
     ]
    },
    { "keys": ["super+ctrl+2"], "command": "insert_snippet", "args": {"contents": "##${0: ${SELECTION/(^ | $)//g} }##\n\n$1"}, "context":
        [
            { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
            { "key": "selection_empty", "operator": "equal", "operand": false, "match_all": true },
            { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
        ]
    },
    { "keys": ["super+ctrl+3"], "command": "insert_snippet", "args": {"contents": "### $0"}, "context":
     [
         { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
         { "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
         { "key": "following_text", "operator": "regex_contains", "operand": "^(?:\t| |\\)|]|\\}|$)", "match_all": true },
         { "key": "preceding_text", "operator": "not_regex_contains", "operand": "['a-zA-Z0-9_]$", "match_all": true },
         { "key": "eol_selector", "operator": "not_equal", "operand": "string.quoted.single", "match_all": true },
         { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
     ]
    },
    { "keys": ["super+ctrl+3"], "command": "insert_snippet", "args": {"contents": "###${0: ${SELECTION/(^ | $)//g} }###\n\n$1"}, "context":
        [
            { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
            { "key": "selection_empty", "operator": "equal", "operand": false, "match_all": true },
            { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
        ]
    },
    { "keys": ["super+ctrl+4"], "command": "insert_snippet", "args": {"contents": "#### $0"}, "context":
     [
         { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
         { "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
         { "key": "following_text", "operator": "regex_contains", "operand": "^(?:\t| |\\)|]|\\}|$)", "match_all": true },
         { "key": "preceding_text", "operator": "not_regex_contains", "operand": "['a-zA-Z0-9_]$", "match_all": true },
         { "key": "eol_selector", "operator": "not_equal", "operand": "string.quoted.single", "match_all": true },
         { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
     ]
    },
    { "keys": ["super+ctrl+4"], "command": "insert_snippet", "args": {"contents": "####${0: ${SELECTION/(^ | $)//g} }####\n\n$1"}, "context":
        [
            { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
            { "key": "selection_empty", "operator": "equal", "operand": false, "match_all": true },
            { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
        ]
    },
    { "keys": ["super+ctrl+5"], "command": "insert_snippet", "args": {"contents": "##### $0"}, "context":
     [
         { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
         { "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
         { "key": "following_text", "operator": "regex_contains", "operand": "^(?:\t| |\\)|]|\\}|$)", "match_all": true },
         { "key": "preceding_text", "operator": "not_regex_contains", "operand": "['a-zA-Z0-9_]$", "match_all": true },
         { "key": "eol_selector", "operator": "not_equal", "operand": "string.quoted.single", "match_all": true },
         { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
     ]
    },
    { "keys": ["super+ctrl+5"], "command": "insert_snippet", "args": {"contents": "#####${0: ${SELECTION/(^ | $)//g} }#####\n\n$1"}, "context":
        [
            { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
            { "key": "selection_empty", "operator": "equal", "operand": false, "match_all": true },
            { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
        ]
    },
    { "keys": ["super+ctrl+6"], "command": "insert_snippet", "args": {"contents": "###### $0"}, "context":
     [
         { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
         { "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
         { "key": "following_text", "operator": "regex_contains", "operand": "^(?:\t| |\\)|]|\\}|$)", "match_all": true },
         { "key": "preceding_text", "operator": "not_regex_contains", "operand": "['a-zA-Z0-9_]$", "match_all": true },
         { "key": "eol_selector", "operator": "not_equal", "operand": "string.quoted.single", "match_all": true },
         { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
     ]
    },
    { "keys": ["super+ctrl+6"], "command": "insert_snippet", "args": {"contents": "######${0: ${SELECTION/(^ | $)//g} }######\n\n$1"}, "context":
        [
            { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
            { "key": "selection_empty", "operator": "equal", "operand": false, "match_all": true },
            { "key": "selector", "operator": "equal", "operand": "text.html.markdown", "match_all": true }
        ]
    },