Online jobs can be stressful, a good aid is to have a calender nearby for deadlines etc. especially when doing this fulltime
If you are a programmer (even in the easier languages such as C#), there's lots and lots of freelance programming sites out there to make use of. Much of the time it's bug correction or small helpful programs for a given company... The payout is okay too if you know where to look
Second life, as mentioned before is also a good bet. The payout may not be steady and may cause red numbers, but if your products are well-made and well scripted, there's a good chance of a decent payout. It requires some modeling, programming and photoshop knowledge however. Once you become good enough at building stuff in SL, you can hire out your services...
Money off internet ads is a good way to make a dime. There's no real risk here, but make sure to read TOSes, EULAs etc. carefully to avoid surprises.
If you have a computer with decent GPU power, you can get started on bitcoin mining. Bitcoins are an open-source digital currency that can be traded for real-world currencies (Like SL's Linden dollars). There's a good wiki describing suitable computer builds for the task (Some larger AMD and many NVidia GPUs use too much power to earn a profit). For a steadier payout, you can join a bitcoin mining pool.
Also you can do jobs for bitcoins, ie. bitcoinjobs.com
1 bitcoin (BTC) = about $3.50 right now
All in all, you can make good money off the internet, but use common sense as many can be scams