I do a mixture of web design/pc repair and ebay selling from home in addition to my day time job. I don't have a monthly income from it as such but last year it must of made roughly £3000 for me and emma (had a nice holiday with it and helping fund another one in 2 weeks time).
Ebay is unbelievably easy to use. My wife has sold numerous items on there now (200+) and made about a £1000 in total over the last 2 years i'd say.
Old clothes ( in her case they look like they've never been worn, probably because she wears about 7 different pairs of clothes a day then washes them and maticulously irons them

), CD's, DVD's etc.
I get a lot of "spare" PC's - really old ones, roughly about 7 years old on average. Strip them down to their individual parts. A quick spray with an air compressor to clean them up and I sell them, I make on average about £80 per machine once stripped and I do this about 10 times a year. Easy money

. I also sell Bluray movies when i'm done with them, old PC games, old Xbox, Xbox 360, PS2/PS3 games - basically anything "electronic".
I've got most of it setup now with Ebay so it only takes me about a minute or so to list an item and I just use a 5 day auction. My Dad ships the items via Courier through his work Free of Charge

but I still charge P&P to cover my supposid costs.
My last sale, a PCI Graphics Card (not even AGP/PCI-E) went for £30 and it cost me £0.
If Ebay isn't for you have you considered something completely different like being a Foster parent - it requires a lot of time and dedication and you get paid and very rewarding. I have strongly considered quitting my current job to do this full time as I have seen first hand what Fostering can be like.
Chris.