Reflexives (intransitive etc.)

In Spanish, these intransitive constructions frequently employ the reflexive form.

The sun dried the clothes. (transitive)
El sol secó la ropa.

The clothes dried in the sun. (intransitive)
La ropa se secó al sol.

For some verbs, the meaning changes when they are used reflexively.

aburrir - to bore
aburrirse - to be bored

acordar - to agree
acordarse de - to remember

acostar - to put to bed
acostarse - to go to bed

casar - to perform a marriage ceremony
casarse con - to become married to someone

despedir - to fire
despedirse de - to say goodbye

dormir - to sleep
dormirse - to fall asleep

ir - to go
irse - to go away, to leave

morir - to die (abruptly, as of an accident, war, etc.)
morirse - to die (as from natural causes; also "to die" figuratively)

negar - to deny
negarse a - to refuse

parecer - to seem
parecerse a - to resemble

poner - to put
ponerse - to put on

probar - to try, to taste
probarse - to try on

quitar - to take away

quitarse - to take off

A few verbs are always used reflexively.

arrepentirse (e:ie) - to repent
atreverse a - to dare
darse cuenta de - to realize
jactarse de - to boast
quejarse de - to complain about

suicidarse - to commit suicide