However, only Battle Royale and Tenjou Tenge are similar to Gantz in terms of nudity and violence. So for you, I recomend those two very strongly.
Death Note and D.Gray-Man are both great, but neither is very similar to Gantz at all.
You could also try to read Hen, which is by the same mangaka as Gantz. They have it here at Stop Tazmo. It contains the same sort of nudity as Gantz, but in my opinion it ain't that good.
I don't see why you try to avoid reading on in the manga though. It is obviously better than the anime, so to me it seems like the anime should follow the manga, not the other way around. Otherwise the anime will ruin the excitement when you read the manga.
I've just ended basilisk I think it is not like gantz 100%,but around 10 - 20%, I really like it,em.... also you can read tokko it is very violent, I don't know..........maybe gyo it is also disturbed,alive,C.A.T,dogs,ice blade(jiraishin,I think it's its japanese name),leviathan and thats all the seinen I have read if I didn't forget some.