I thought I'd post a nice long list of fanfic recs for everyone. :) I took the ones from my favorites list and then went on a massive search for others. They range from G to R so there's something for everyone.
Idiomatic by Lys ap Adin
Rating: G
Gen
Summary: Sometimes it's a good idea to choose one's words wisely.
Note: ...it's really just a small crackish drabble but it's entertaining either way and it's got the three of them having fun together...at Gokudera's expense.
Uncontrived Loyalties by Swiss Army Knife
Rating: G
Gen
Summary: In spite of everything, Tsuna and Yamamoto dramatically increase Gokudera's life expectancy
Note: This one is so sweet and beautiful it could bring tears to your eyes and I'm not joking. It's stories like this that make me love these three so much.
What Remained Unseen by windlily
Rating: PG
Gen
Summary: Inspired by Chapter 155. "Yamamoto said the same thing. And he also said many, many good things that he said not to tell Gokudera." Tsuna and Yamamoto discuss the crippling fight against Gamma.
Notes: Very well done. I've always wondered just what happened when Reborn said that.
Costs and Benefits by Lys ap Adin
Rating: PG
Gen
Summary: What could be more important than baseball?
Notes: This is an Eyeshield 21 crossover...so I don't know much about that half, but for those that do I'm sure that you can appreciate it.
Our Promise by manmannikuman
Rating: PG
Gen
Summary: A short friendship fic, involving the three young men; Yamamoto, Tsuna and Gokudera.
Notes: It's graduation time, and the three look back in order to move forward. Cute and touching.
Decade Dilemma by daigranon
Rating: PG
Gen
Summary: A curious Gokudera and Yamamoto try to use the Ten Year Bazooka on Tsuna. After some improvisation they succeed, and are blown away by what they see.
Notes: I wish this would happen in the canon. Who doesn't like TYL!Tsuna? And there's a bit of Hibari thrown in.
Sous Entendre by Hitokiri-san
Rating: PG
Gen
Summary: Yamamoto is troubled by how little sense Tsuna's dying words make.
Notes: Rather sad because it's dealing with Tsuna's death and how Yamamoto and Gokudera are trying to deal with it. Angsty, but good.
Those Nights by Ashinan ♥
Rating: PG
Gen
Summary: Those nights, when we were together, when the hardships in our lives were forgotten; those nights kept me going. And they kept me alive.
Notes: THIS IS BEAUTIFUL!! Seriously--I can read this over and over again. Great portrayal of their friendship and great homage to these three. It's basically a timeline of different sleepovers throughout their lives with scary movies. What more could you ask for?
Off to the Side by music nimf
Rating: PG
Gen
Summary: For the first time, Tsuna feels like the third wheel.
Note: Actually rather sad and depressing, but it's interesting and a good read at the same time.
Living by lewdness
Rating: PG-13
Gen or Slight Romance
Summary: They're just living through it all as best as they can.
Notes: I can't say too much without spoiling it, but it's about them when they're older and it's fun to read.
Wishes by lewdness
Rating: R
Romance
Summary: The universe doesn't just let you get away with upsetting its grand design. It requires payment.
Note: Really sad, but very sweet. I like how there is a focus on other members of the Family as well.
A reminder that the three fics mentioned in a previous post are also very good as well! If you haven't checked those out yet be sure to!