Window cleaning
Pick a street in a decent but not top of the range area (Upper middle class terraces are good)
Leaflet them all on the Friday, Call in Saturday and offer to clean windows on a Saturday morning
Next week pick another street, after 4 weeks back to the first street and hit them again - It will take a while to build up but you might end up with a quarter of the street after a few months.
Hedge trimming and lawn cutting service
As above, location, location, location, picking the area is critical - Think of all the holiday homes on the Broads. Who does the gardens ? - talk to the letting agents.
Painting and decorating - helps to have a friend in the business professionally and go along as the painters mate
E-Bay - Have a good clean out of your stuff, and then start buying at boot fairs for onward selling.
Only buy/sell what you know about (ie bike spares ??)
Web Pages for local businesses and organisations - If you have the ability and the time.
Whilst the local butcher and baker may not give you the time of day, the local Scouts, WI, Save our local ....., the Steeple fund, Schools etc may, if the money is right, be interested, as they are all short of money it's not the £500 up front they can afford, but if you make and then host and maintain their website they can afford a monthly subscription which if you get enough of them can be a nice little earner on the side, but takes a bit of effort to get going.
Talk to the local letting agents.
They often have a need for people to go and do house inventories and inspections. Get hold of some copies first so you know what is involved, it's not difficult but you need to be very detailed.