brief, little, quick, short
Just a quick note to wish you luck.

handwritten, scribbled
cover (AmE), covering (BrE), credit, delivery (BrE), love, promissory, ransom, sick (BrE), suicide, thank-you
Post-it™, sticky (esp. AmE)
Never write your password on a sticky note!

crumpled

scribble (sb), write (sb)
send (sb)
leave (sb)
She left me a note to say my dinner was in the oven.

pass
I saw you two passing notes during class.

sign

a note of thanks

brief
copious, detailed, extensive
lecture
field
case, clinical (esp. BrE), medical (esp. BrE)

jot down, keep, make, take
She kept detailed notes of her travels.

go through, look through, read through, sift through
compare (usually figurative)
Let's compare notes on our experiences.

note of
I've made a note of the book's title.

note on
The booklet has full notes on each artist.

make a mental note (of sth/to do sth)
She made a mental note to call them in the morning.

detailed, extensive
explanatory, helpful, informative
interesting
introductory
marginal, side
biographical
booklet, liner, sleeve (BrE)
briefing (esp. BrE), programme/program

five-pound, ten-euro, etc.
crumpled

bundle, roll, wad
a thick wad of notes

high, top
She's a little wobbly on the top notes.

low
right
wrong
musical
dissonant
whole, half, quarter, eighth, etc. (all AmE)

play, sing
hit, strike
hold

brighter, cheerful, happier, hopeful, lighter, optimistic, positive, upbeat
On a brighter note …

related, unrelated
On a completely unrelated note …

discordant, false, sad, sombre/somber, sour
faint
a faint note of bitterness in his voice

serious
right
His opening remarks struck the right note.

odd
cautionary, warning
He sounded a cautionary note.

personal

hit, sound, strike
inject, introduce
His remarks injected a note of levity into the proceedings.

detect
I detected a faint note of weariness in his voice.

end on
The conference ended on an optimistic note.

creep into sb's voice, enter sb's voice

note of
A note of suspicion entered his voice.

a note in sb's voice
There was a sad note in her voice.

careful

take
He took careful note of the suspicious-looking man in the corner of the bar.

worthy of note
The sculptures are worthy of note.