Some stuff worth checking out:
"Hl Opposing Force - Firestorm : Another reality.Another experiment.Same objective.Save yourself from the depths of Black Mesa and rescue the personnel from hell's outbreak in this thrilling HL1:Opposing Force mod."
Created by 23-Down
"Half-Life: The Infected : Have you ever considered who else was in the same HEV suit?Who else fought for survival in the aftermath of Black Mesa's resonance cascade?Play as Dr.William Jones in this deeply story-driven mod for Half Life 1."
Created by Neclipse
"Half Life - Deflections : You thought security duty was easy?Reconsider it as you play a security guard sworn to serve and protect the facility's personel.But what happens if it comes to your safety?Find out in this classical action Half Life 1 mod."
Created by Thanoshltbeginning
And also, for all you Americans: