Phazon Suit (Metroid Prime); limited to blue Phazon
Ibara Naruse, Aoi Fukasaku and Taeko Nomura (Coppelion) have been genetically engineered to be impervious to radioactivity, making them able to enter any radiation zone with no harm.
Due to decades of exposure to Earth's Sun, Kal-El/Superman of the Kingdom Come universe (DC Comics) has developed an immunity to Kryptonite.
As they are immune to all sorts of contaminants, the Fork Maidens (New Blood Interactive's DUSK) are also immune to radiation, and its effects on the physical body.
As a sub-power to having immunity to contamination, Possessed Scarecrows (New Blood Interactive's DUSK) are immune to radiation of all kinds.
As simply air that was shaped and animated to life by Mental, the Air Elementals (Serious Sam) are immune to radiation of all kinds.
Homer Simpson (The Simpsons) seems to be immune to nuclear radiation, as he simply shrugged off the radiation after emerging from a meltdown he caused, and even ate nuclear waste as a punishment with no ill effects.
The Scout (Team Fortress 2) can drink bonk, radiation and sugar filled drink with no ill effect's.
The Thals of Skaro (Doctor Who) had developed a drug which made them immune to the intense radiation caused by their war with the Kaleds.
After her suit was corrupted by Phazon, Samus Aran (Metroid Prime) wore the Phazon Suit which protected her from blue Phazon, but not the more lethal red Phazon.