The North Tongue west of Burgess Junction can be good. Might also consider the Middle Fork of the Powder west of Kaycee; fishing the river requires hiking into a canyon so you have to be in halfway good shape.
Seven Brothers Lake west of Buffalo. Seven lakes fairly close together, you will see some people there, esp. this weekend. If you had some more time there are several lakes that would be worth hiking into in the Cloud Peak Wilderness.
For a couple days fishing the Middle Fork Powder may be your best bet. Or, you could always fish the North Platte west of Casper.
ClearCreek