in Ajax there isn't a whole lot... the closest spot would be Duffin's Creek. near the mouth, in the marsh area (back bays), you can get lots of carp and catfish, i have caught a couple bass and pike there as well. up the river in the spring you can get rainbow trout, and in the fall you can get salmon.
the closest lake (aside from Lake Ontario) is Lake Scugog near Port Perry. you can get panfish (crappies, perch, bluegills, pumpkinseeds, rockbass), bass, walleye, muskie, carp, catfish.
PM me if you want to meet up sometime... we're living in the same town!