Altered States by Sleeps With Coyotes
Pairing: Roy x Ed, Ed x Roy
Warnings: Yaoi, smut, Nc-17, leaves you hanging

Okay, so the key to this fic is that at first you're like "Ed is making an array," and then you're like "Oh, Roy is---Roy is getting naked," and then things get smutty and you think "Alchemical Sex?" and then the plot kicks in and all you can think is "Oooooh." Now this probably sounds absolutely retarded to you, but trust me -- this is the best melding of sex and plot I've ever seen. They're so melded that the sex is the plot, and yet the plot is something entirely different, smart and very, very interesting. The only problem I had with it is that it finishes and leaves you hanging - I just have to go see if there is a sequel.
Also has sequels you should read in order.

...And honestly, just read everything she has ever written. Because she writes more than just anime, and more than just FMA. Seriously. Go fangirl yourself to death.

Research by Jaelle
Pairing: Roy x Ed, Al x Winry
Warnings: Bust a gut cute

Tonight is Al and Winry's first date, and he wants to share a perfect first kiss with her. But how to make it perfect without prior experience?
Through research.
[link routinely changes. Just go to the main archive.]

Must Like Cats by girl_starfish
Pairing: ?? Some Roy x Ed(xAl?), some Ed x Hawkeye
Warnings: none

You really can't replace someone no matter how much you try. But the Elrics are smart and have decided that they will find a shared girlfriend. Ed can do the kissy stuff and Al can do other stuff, since he doesn't have a body yet. So they place an ad in the newspaper listing some of their basic requirements.

Fast Work by Kristen O.
Pairing: RoyxEd
Warnings: hillarious

What can I say about this? It's pretty short, and it's a humour piece, but it's also smut. Kind of indirect smut, or maybe direct. It's hard to tell. Suffice to say it had me giggling all day at work and I just-couldn't-stop. AMAZING.

Assessments by Harukami
Pairing: Roy x Ed
Warnings: none

Mmm, it's smutty smutty goodness.  The yearly assessments are coming up and Roy and Ed both need to study, so Ed decides to stay at Roy's in order to make use of his library. Things develop. >_> You know. Smutty, delicious things. XD

Snow by Harukami
Pairing: Roy x Ed
Warnings: None

A snowball fight between Roy and Ed. Very fun.

Proper Communication by Harukami
Pairing: Roy x Ed with various other background pairings
Warnings: I've given up warning for sex now.

It's smut. It's super smut, it's delicious and it's...it's good. It's Harukami. Everything by her is good!

Incentive by ninkasa
Pairings: Roy x Ed
Warnings: none

Roy is jealous, Ed is confused. XD Fun, funny and yuuuum.

The Adventures of Roy Mustang: Sex Ed Teacher by Sky_Dark Pairings: Roy/Ed

It took me awhile to sit down and read this because I thought it was AU and I wasn't all that interested. (Teacher/student things normally do nothing for me.) But it's not. It's right inside the series, so much so that I haven't been able to read the most recent chapters because they have spoilers for things I haven't seen yet. Damnit.

The main focus of the fic is that you should feel both absolutely -terrible- for Roy because even if he's sleeping with Ed, Ed is -crap- in the sack, but at the same time, he loves it and you love it and it is hillarious and witty and fun.

Easy Like Candy by Sleeps with Coyotes [Roy/Ed UST]
Totally not what I thought it was, but -hillarious-. It reads just like something that could happen in a filler-episode of FMA, but the point is the reactions of everyone around Roy and Ed. The boys themselves are completely clueless, but full of fun action that just makes you laugh. XD Excellent, excellent stuff as usual.

Kitten Tales by Tir-synni [Roy/Ed but totally not the point]
Ed -finally- understands the use for kittens. And he -loves- it. Predictable but so, so good. Consider it fanon-- they're OOC but you don't care because it's all just a set up for the punch-line.

Library Cat by Sleeps with Coyotes [Roy/Ed referenced]
It's fourth in a series of crack-shorts Coyo's been writting on and off, and...I love them. I don't even know why, but I love them and they're funny and cute and just hillarious and really, really make me miss my cat. On a side note, you don't even have to like cats to love these. You just have to die of laughter.