Bryan --
The nonsport Net54 site has galleries of most N and T sets, if you know where to look. Here are the T29 Animals cards, which are very affordable:
http://www1.coe.neu.edu/~dan/T29/go.html
T42 and T43 Birds, also affordable:
http://www1.coe.neu.edu/~dan/T42/go.html
http://www1.coe.neu.edu/~dan/T43/go.html
T58 Fish, ditto:
http://www1.coe.neu.edu/~dan/T58/go.html
In the 19th century, Allen & Ginter put out several nice sets, which are going to set you back more than the T cards, but not nearly as much as baseball N cards from that era. Here are N25 Wild Animals of the World and N21 Quadrupeds:
http://www1.coe.neu.edu/~dan/z-ns-N25/go.html
http://www1.coe.neu.edu/~dan/N21/go.html
N4 Birds of America, N5 Birds of the Tropics, N13 Game Birds, N20 Prize Chickens, and N23 Song Birds:
http://www1.coe.neu.edu/~dan/N4/go.html
http://www1.coe.neu.edu/~dan/N5/go.html
http://www1.coe.neu.edu/~dan/N13/go.html
http://www1.coe.neu.edu/~dan/z-ns-N20/go.html
http://www1.coe.neu.edu/~dan/N23/go.html
And N8 Fish from American Waters:
http://www1.coe.neu.edu/~dan/N8/go.html
There were also larger-size A&G sets of Birds of America (N37), Birds of the Tropics (N38), Fish from American Waters (N39), Game Birds (N40), Quadrupeds (N41), and Song Birds of the World (N42).
http://www1.coe.neu.edu/~dan/N37/go.html
http://www1.coe.neu.edu/~dan/N38/go.html
http://www1.coe.neu.edu/~dan/N39/go.html
http://www1.coe.neu.edu/~dan/N40/go.html
http://www1.coe.neu.edu/~dan/N41/go.html
http://www1.coe.neu.edu/~dan/N42/go.html
The larger-size cards are more expensive. I have at least one example of each of these Allen & Ginter cards (and in fact of all of the A&G color sets).
Other 19th-century tobacco companies put out occasional animal sets, such as Duke's Fishers and Fish (N74, N108), Goodwin's Dogs of the World (N163), and Kinney's Animals (N216) and Butterflies (N217).
http://www1.coe.neu.edu/~dan/z-ns-N74/go.html
http://www1.coe.neu.edu/~dan/N108/go.html
http://www1.coe.neu.edu/~dan/z-ns-N163/go.html
http://www1.coe.neu.edu/~dan/z-ns-N216/go.html
http://www1.coe.neu.edu/~dan/z-ns-N217/go.html