There are plenty of good trade routes, but it really depends on your ship. If you have a small ship, pick out a really profitable long run to maximize your PPU - if you have a vast cargo hold, why risk, your assets? You can make a tidy profit by just jumping between 2-3 different systems in a circuit.
I personally like the Bretonian circuit involving Prisoners, Gold, Refugees, Basic Alloys, Ship Hull Panels, Luxury Goods and VIPs. There aren't huge margins, but it's relatively safe and short and whilst not strictly in RP for my hauler pilot (the prisoners and refugees aren't, but they can be justified!) it all works well.
