These aren't the "5 best fics," by the way. Sometimes the one that makes you think most fondly of your time in a fandom is not the best, just the most special for some reason.
Sirocco, D.L. Witherspoon
When Carolyn runs afoul of bioterrorists, she heads for the one safe place she knows--the arms of her ex-husband. There is action, h/c, and character death, plus Jim/Carolyn... and it's one of my all-time favorite stories.
Out of Harm's Way, by K. Ryn
Written by one of the masters of TS h/c fic, this is a classic that includes poison, a mystical bond between Sentinel and Guide, and some excellent friendship moments.
Imperfections series (9 stories), by Dasha ( dashamte )
If Blair's washing out of the Guide program, who's taking care of Jim? AU.
To see my full squee-ish review of this series, click here. It's one of the best versions of the AU "sentinels and guides are known" trope that has been written, and Dasha's take on canon events and hypersenses are wonderful.
Sometimes You Feel Like a Nut, by Red Soprano
Always guaranteed to make me grin, this fic also helped inspire one of my first TS fics, "L-O-Y-A-L-T-Y."
Mail Bonding, by Shelly
My favorite out of the domestic roommate fics, although I had to hunt a bit to find it, because I couldn't initially remember who the author was!
Evolution, by D.L. Witherspoon
Hijacked!, by D.L. Witherspoon
It's Hot and I Hate You, by Jael Lyn
Holding It In, by kerravonsen (aka "a portrait of another universe's Blair")