Harbor Freight has a couple of VERY nice seal/bearing install kits with an assortment of aluminum disks. (The aluminum won't damage steel bearing races.) I have the one with the different colors of anodizing, and it's been extremely useful for banging in bearings and seals many times, and I've also used it with my hydraulic press several times.
That said, sometimes the situation calls for different means, especially when there's a shaft in the middle. When installing a crankshaft oil seal on one of my motorcycles, I used a large socket, a long bolt threaded into the crankshaft, and some nuts and washers to push the seal into place. Worked great. You can do the same with many car cranks, camshafts, etc.
I once had to install a large seal into the rear end of a shaft drive motorcycle. A visit to the bLowe's plumbing department with the seal in hand yielded a PVC adapter that fit perfectly, and the seal went right in with a block of wood and a rubber hammer.
Improvise and adapt...