Sleep for free:
If you lack the cash to pay for a night in the inn/fines, or just don't feel like paying at all, go into a house & sleep in their bed. Run outside before the screen turns black & you won't be charged for trespassing.

Increase your property value & make a profit:
1. Buy a house with more than one trophy mount (or upgrade if necessary).
2. Mount the two most expensive trophies you have.
3. Smash the door down.
4. Sell the house. (Note the profit)
5. Go back inside and collect your trophies.

Lather, rinse, repeat as needed.

Get Money Extremely Fast:
In Oakvale at the item store the shop owner sells Emeralds for about 350 gold each, and he has 37 of them. Buy them all so they will be all for the same price. Next go back to the beggining of the shop choices and choose to sell back to the same guy, and sell all the Emeralds for 700. Since he has none of them in stock, if you choose to sell them all at once he will give you 700 for each of them, and this can be repeated as many times as you like. I have already made over 250,000+ gold doing this. It is very fast.

5 Augmentations on Frying Pan:
The Frying Pan, which you get at the end of the treasure hunt, actually has 5 aug slots, though the game only shows 4. Once you put in 4 augmentations you'll still be able to attach one more though the game shows the weapon as full.

Hero Save Exploit:
In the middle of a quest, if you use a hero save and reload the save, you will start at the beginning of the quest as if you had never begun, and you will retain all items that you obtained during the last run of the quest. This is especially useful in the Arena, where vast amounts of money can be made if used right. This exploit can also be used to get infinite silver keys, potions, etc if used during missions. Be careful not to use this exploit too many times as it can damage your save.