I know I'm a bit late for this, but in regards to today's picture, there's a really easy way of angling your side-smashes in Brawl: basically, perform a smash attack with the C-stick while tilting your control stick up or down to angle it accordingly. It's very simple to do and doesn't require you to tilt your control stick diagonally.
Here are all the characters in Brawl that can angle their moves:
-Mario (f-tilt, f-smash)
-Luigi (f-tilt, f-smash)
-Bowser (f-tilt)
-DK (f-tilt)
-Diddy (f-tilt)
-Yoshi (f-tilt, f-smash)
-Wario (f-tilt)
-Zelda (f-tilt)
-Ganondorf (f-smash)
-Samus (f-tilt, f-smash)
-Zero Suit Samus (f-tilt)
-Ice Climbers (f-tilt)
-Kirby (f-tilt, f-smash)
-Captain Falcon (f-tilt, f-smash)
-Pikachu (f-tilt)
-Jigglypuff (f-tilt)
-Squirtle (f-tilt)
-Charizard (f-tilt) *unsure about this one*
-Lucario (f-tilt)
-Fox (f-tilt)
-Falco (f-tilt)
-R.O.B. (f-tilt, f-smash)
-Ike (f-tilt)
-Ness (f-tilt)
-Lucas (f-tilt)
-Sonic (f-tilt, f-smash)
I hope I didn't miss anyone.