I have come across a lot of stamps that are 1, 2, 10, 15, 25, 33, 34, 37 cents. Am I able to still use these for postage?

I don't see why you couldn't use them for postage. I mean, we still do have old money in circulation that is still being used. However, the Postal Service would know better. You also might want to see if any of the stamps have a value beyond that of their current value as postage. It sounds like you have some that are pretty old.

For instance, just for the possible collector's value for a 10 cent stamp, you might want to have a look at the following site: United States Stamp Price Guide 1940-1945 -United States Stamp Values

yes, they are still worth their face value, you will just have to put enough on, to equal the current value of postage