C340 pilot reports missing a NOTAM establishing a TFR along his VFR route of flight.

Narrative

I was flying a Cessna 340 for currency and I had checked the weather; NOTAMS; TFR's; and all other information I thought was pertinent. I checked the information using three different websites. I had filed an IFR flight plan to and from an airport but the weather was a clear and I never get the chance to fly VFR so I thought it would be a nice change to enjoy the day without the normal IFR restrictions. On the way home I was teaching a student and because of traffic and ATC being a little busy on the radio; I did not pick up flight following or my IFR clearance and continued enroute. I did have traffic avoidance; terrain; and weather onboard the aircraft and as I continued to teach I became complacent that there was no reason to contact ATC as we had already leveled off and the flight would be rather normal. It wasn't until after I landed and was instructed to call Approach Control that I thought anything had gone wrong. I was told to call Indy Center who told me I had violated a TFR. I checked a different web service and there was one TFR I had missed. I usually will call flight service for any NOTAMS or TFR's that I might have missed on the internet; and that was one of the few days I did not. There is a benefit to flying on a flight plan; ATC usually will keep you clear of any MOA's; TFR's; restricted areas and any other hazards to aviation. ATC is not a fail safe; but I strongly urge everyone to always check with FSS for any updates and not rely solely on the internet for all information for your flight. There may be something you are missing that may keep you safe. Also; use all available services at your disposal. It may seem great to relax and not talk to ATC; but that communication could save you some headaches and even save your life.