I have really liked the SPIGEN Ultra Fit case. It is very slim and the plastic is very tough without being brittle. I use the black one and it has a matte finish similar to the matte finish of the Nexus 5 itself.
Ballistic cases for the nexus 5 are still available at a lot of cell carriers in Canada. I use a skin myself, my partner uses a grey and black ballistic I just bought her new last week at my local Koodo kiosk