[Ctrl]B, [Ctrl]I, [Ctrl]U
Highlight your text, press [Ctrl]B to make it bold. [Ctrl]I will make your text italicized. [Ctrl]U underlines your text.
Change fonts and formatting without using Format | Font. Highlight the text you want to change and press [Ctrl]T. To change the text on your entire presentation, highlight the slides in the task pane and then press [Ctrl]T to open the Font dialog box.
If you need a different font size, use these shortcuts to increase or decrease the size. For example, if you highlight a block of text in your presentation and use [Ctrl][Shift][>], you'll increase the font by the same increments found in the Font dialog box. If you want to decrease your font size, [Ctrl][Shift][<] will take it down.
Highlight text and use [Ctrl][=] to apply subscript formatting. Press [Ctrl][Shift][+] to apply superscript formatting. (Handy, especially for math/chemistry related presentations!)
This shortcut changes the text case. For example, if you type "this is fun" but want it in all caps, highlight the text and press [Shift][F3] to change the case. Hitting it once will capitalize the first letter of each word. Hit it twice and the entire phrase is in all caps.
Highlight your text and press [Ctrl]E to center a paragraph.
If you want to embed a link to a webpage in your presentation, highlight the text and press [Ctrl]K to bring up the Edit Hyperlink dialog box.
Do you need to produce more than one PowerPoint presentation? [Ctrl]N starts a brand new one quickly.
Just as in Word and Excel, you can use Find [Ctrl]F and Replace [Ctrl]R to search for and correct words in your presentation instead of correcting each one manually.
Ready to send your presentation out before your students or other audience? Use the [F7] key before you show off your presentation to do a spell check.
Need to add lines, shapes, or a flowchart to your presentation? [Alt]U will open AutoShapes on the Drawing toolbar.