Like I said TONS of variants.
1891 Mosin Nagant Infantry Rifle (the origional Mosin)
Dragoon Mosin Nagant (intended for mounted infantry)
Cossack Mosin Nagant (simular to Dragoon, but was sighted for use without the bayonet)
1907 Mosin Nagant Carbine (11.4" shorter then the 1891. The stock went almost to the front sights, so it did not us a bayonet)
1891/30 Mosin Nagant (the rifle many of us have. Most Dragoons, were converted into this.)
1938 Mosin Nagant Carbine (8" shorter then the 1891/30. Meant to be used by troops that would see very little combat if any)
1944 Mosin Nagant Carbine (simular to the 1938, but had a permanently affixed, side-folding cruciform-spike bayonet.)
1891/59 Mosin Nagant Carbine (A shortened version of the 1891/30. The rear sight numbers were ground off, but other then that it is very simular to the 1938)
And that is just the Russian Variants! Many other countries had their own variants too.
I want to collect them all.
Here is a good list of them (about half way down the page) http://en.wikipedia.org/wiki/Mosin%E2%80%93Nagant#Russia.2FUSSR