Some sonatas to start with:
k30 in G Minor (cat's fugue)- not that difficult, quite polyphonic in texture, a very interesting piece.
k54 in A Minor- not too difficult, powerful, some octaves and wide spaced arpeggios. Don't play the arpeggios with a clingy touch, allow your left hand to leave the surface of the keyboard. Some hand crossing, not too tricky.
k87 in B Minor- the most beautiful of the slow sonatas. Needs flexibility and a sensitive touch. Some quite different editions. Use the urtext if possible.
k135 in E- joyful, lovely piece, with some trickier crossing of hands (a favourite Scarlatti technique).
k198 in E Minor- some skips and hand crossing, an almost passionate work. Not that difficult.
k260 in G- a great piece, some leaps.
k319 in F#, beautiful, mercurial. Not that hard to play, but tricky to read (lots of changes of key and accidentals). The 'internal' ornaments can be tricky for some.
k402 in E Minor- few traps in this one. very 'Spanish' in feel.
k466 in F Minor- I love this, haunting theme.
k480 in E- a famous sonata, has some repeated chords and fast repeated notes, inverted mordents for the left hand thumb, and is thus a little trickier than it looks.
k491 in D- well known, attractive, spirited, with some wide spread arpeggios and passages in 3rds.
K513 in C- lies under the fingers well.
K531 in E- gorgeous piece of pianistic melody, similar in style to k135, but with more pathos and less exuberance.