I used to fish for SMB on the SB Raritan a lot during the last few summers, action picks up below Clinton. Walk a lot and cast a lot and you'll be able to hook up some nice ones. The entire length down to Duke Island Park is easily accesible, you just need to pick up a map and explore.
I also fished the NB in North Branch Park/fairgrounds just off 202. Again, walk and explore (head from the upper parking lot upstream along the river, there are some really nice holes).
Also, Duke Island has some smallies if you know where to look for.
But by far the best SMB action is on the Big D...