In real life, we don't have conspicuous, over-taxed speaker attributions telling us how people are feeling.  As humans, we're hard-wired to read the body language of everyone around us, and we constantly assess their emotions on a subconscious level.  

This is possible in fiction as well.  The strongest place to express character emotion in a scene is dialogue.  The second strongest place to put emotion is in beats--moments of body language surrounding the dialogue.

Bob ran his hand up my thigh.  "You're so fucking hot."

Punctuated and paragraphed properly, beats often eliminate the need for speaker attributions entirely.  That doesn't mean you should use them all the time, because a passage too full of beats takes on a stop-start rhythm that itself becomes conspicuous, and conspicuousness is what we're trying to avoid.

I find that 2-3 beats per 10-15 of dialogue is about all you can get away with, though there are surely exceptions.  In general, I recommend a single speaker attribution or beat at the beginning of a two-speaker conversation, and then let the seesaw rhythm carry for as long as it can--usually no more than 5-6 lines before I feel the need to sprinkle in some setting or internal monologue.

If you've got three or more speakers, you'll need either an attribution or a beat attached to every line, so I tend to shoot for about one part body language to two parts "said", and I try to keep three-plus conversations as short as possible.  They're hard to write, and harder to read.

How you write beats--and how many you use--depends somewhat on your POV.  I tend to favor intimate third person in my work, so often what I do is simply describe a bit of body language...

He leaned forward.  "Keep talking."

He thrust out his chest.  "What are you looking at, bro?"

...and let the reader fill in the emotional blanks just as they do in real life.  This has two benefits; 1) the language is immediate and inconspicuous, and 2) it actually pulls the reader deeper into the story by allowing them to participate in building the story world.

In first person, you have the benefit of full intimacy with a single character, so if your POV character has a conscious thought about the speaker, you can work even more layers into the dialogue:

He thrust out his chest.  "What are you looking at, bro?"What a douchebag! "Nothing, sorry."

This not only tells you more about the speaker, but more about the POV character.  The POV character in the above example clearly has a much different personality than the one in the following example:

He thrust out his chest.  "What are you looking at, bro?"Intriguing, how simian dominance behaviors have yet to be bred out of mankind. "Nothing, sorry."

I find, in an intimate third person POV, you can pretty much write internal monologue just as you would in first person, but it behooves the story to keep them to a minimum.  If we pause for our POV character to appraise every line of dialogue, the story fails to proceed.  Moderation is good in first person too, but you have a little more leeway.

Another issue worth pointing out is that when you rely more on body language than attributions, you allow your dialogue to remain grounded in the scene.  Any body language is great, but if you focus solely on people's facial expressions, posture, etc., you'll quickly find that you have tons of scenes where people are constantly grinning, or frowning, or running their hands through their hair, or leaning forward.  The best thing to do is to craft body language that shows characters interacting with the setting around them.

Say you have a heated argument between two lovers.  You could just write them sitting on the couch, or in the bedroom, and they could bandy wits to your heart's content.  But the scene could be spiced up considerably by having them do something.  Could this argument take place during a couples golf tournament?  How about in the middle of cooking dinner (which would give them plates and sauce pots to throw...)?

Any time you can attach a setting to your body language, you not only wind up with fresher, more original body language, you end up with more realistic settings.  Big, thundering blocks of description can be fun to write, but they're...less fun to read.  They're best kept to your notes.  Readers don't remember that stuff anyway. What readers remember is people doing things.  A character acting on an object makes that object real, and invites the reader to fill in all kinds of details surrounding that object.  It's one of the basic ways to show and not tell.

Between beats and good-old "said", you should have 99% of dialogue situations covered.  Sticking to these inconspicuous devices will help you develop that strong, fluid style that keeps readers locked in your story.