They can do more than just tell the reader who is speaking
Speech tags can be as simple as said or as complicated as three paragraphs of hand motions. Said is best used, in my humble opinion, when the dialogue is important and you want the reader's full attention. Hand motions and facial expressions are good for emphasizing how characters respond to the dialogue or even just for exhibiting mannerisms that help establish their character. This list includes speech tags that I've found in various works and the only reason for maintaining this list is so I can occasionally browse through it when I'm searching for just the right way to describe something and I think said isn't quite the right word.
Adding adverbs allows the author to convey emphasis and feeling and can be an excellent device for conveying how the person speaking feels or even how the person hearing the words thinks the person feels. The author needs to be cautious, however, in the use of adverbs after the word, said as this can degrade into Tom Swifties. [Yes, Tom said swiftly.] They should be used sparingly and appropriately.
Said Michael, in an extremely neutral tone.
Other says of adding more depth include all of the following:
Same arctic voice
he began, and stalled
in a tone of mild encouragement
fell into a digestive silence
noted with dark amusement
He went on more confidently
In a decidedly odd tone
Cleared his throat, and began
Sputtered, momentarily beyond words
Crying openly now, thin strained sobs
Reporting how the person responds to the last line said can also convey a great deal
Looked quite stunned, his mouth slightly open.
Leaned forward, staring avidly
eyed him dubiously
Screwed up her mouth, and shook her head
Raised an inquiring eyebrow at this
Looked indignant, then blinked
Studied Michael dubiously, shrugged, and advanced toward the bay window.
Nodded and withdrew
Sighed bitter agreement
Shot him an annoyed, wary look
Smile faded from wry to pensive
Looked pleased, watching him fold so neatly
Let him burble on until he ran down
Renewed wariness closed down the expression on his face
She looked away from him. Mumbled diffidently...
Her expression was disturbingly fey
His answering smile seemed to lighten his eyes
Sincere, if daunted confusion
Hand gestures include:
Opened her hands back to him
Gestured to the chair opposite him, across the low table
Tented his hands in a gesture of reason
In a supremely sinister gesture...
Waved it away
Gestured helplessly, and gave her an earnest look
Body language includes:
His eyes narrowed
Lips twisted in sympathy with her expression
Tried to rub the involuntary smile from her lips, and failed
Wrenched a short little nod from her and a brief, bleak
Walked backwards a moment, watching her retreat. She strode on, head down, and didn't look back. Shaking his head, Michael passed out of sight.
Inspired to a touch of malice, Michael let his brows climb
Kept his expression to no more than a faint, slight smile.
Rubbed his chin
lips were tight and eyes a little blurry as he digested Michael's words
Stared at her in astonishment, his lips moved on one or two tries at speech, before his mouth at last made it into motion.
Seated himself a little stiffly as if not altogether comfortable
Smile remained fixed
Eyed Michael in growing conjecture
Smirked, obviously satisfied at Michael's dismay
Pressed his lips thoughtfully together
Gritted his teeth
Pursed his lips, then tried not to smile too broadly
Looked at him inquiringly
Face softened at the mention of her name, and he paused, an odd smile playing on his lips
His face stiff
eyed her with extreme wariness
The unacknowledged panic which had gripped his throat for weeks seemed to ease, as he stared out into the sunny scene below.
Hesitated, his stomach tightening in distaste for the task ahead
*****clutching for coherence in her seething brain
Methods of announcing someone approaching:
Voices drifted up from the entry hall.
Voices carried faintly from the house through the open windows into the back garden, too muffled to make out the words. One was a low-pitched male rumble. The other was...