Ctrl+Alt+V, then T and Enter

Copy a cell via Ctrl+C, then via Paste Spacieal, paste format of that cell to current cell

Alt+Enter

Repeat a previous cell format action on current cell

Ctrl+1

Open Format Cells dialog with last selection active

Ctrl+Shift+F

Open Format Cells dialog with Font Tab active

Ctrl+B

Apply/ remove bold format

Ctrl+I

Apply/ remove italic format

Ctrl+U

Apply/ remove underline format

Ctrl+5

Apply/ remove strikethrough formatting

Alt+H, FF

Home select Font Face; type font name supported by auto-complete, or use Arrow Down to select.

Alt+H, FS

Home select Font Size; use Arrow Key, then Enter to change size

Alt+H, FC, Escape, Enter

Assign current font color to selection via Home Font Color. While escaping the font-color drop-down, the focus stays on the icon; simply press Enter to assign the current color.

Alt+HH, Escape, Enter

Assign current fill color to selected cell color via Home Higlight Cell. While escaping the highlight drop-down, the focus stays on the icon; simply press Enter to assign the current color.

Alt+HH, then N

Set to No fill color

Ctrl+Shift+~

Apply the general number format (e.g. 1000)

Ctrl+Shift+1

Apply the number format with two decimal places, thousands separator (e.g. 1,000.00)

Ctrl+Shift+2

Apply the time format with the hour and minute, and indicate AM or PM

Ctrl+Shift+3

Apply the date format with the day, month, and year

Ctrl+Shift+4

Apply the currency format with two decimal places (e.g. $1,000.00)

Ctrl+Shift+5

Apply the percentage format with no decimal places (e.g. 10%)

Ctrl+Shift+6

Apply the scientific number format

Alt+H, AL

Align Left

Alt+H, AR

Align Right

Alt+H, AC

Align Center

Alt+H, AT

Align Top

Alt+H, AM

Align Middle

Alt+H, AB

Align Bottom

Alt+H, W

Wrap or unwrap text (Home - Wrap Text)

Alt+H, MM

Merge cells - Merge

Alt+H, MU

Merge - Unmerge

Alt+H, MC

Merge and Center

Alt+H, MA

Merge Across (merge all columns, but not rows in selection)