Suzuki SV650. Popular bike for folk starting off. Know many people, including me that had one as their first. Cheap to run, forgiving (for a motorbike). Being a V twin it's plenty torque to pull you out of trouble when you select the wrong gear or are just wanting to be lazy. Proven mechanicals. Available naked or the S version has plastic. SV1000 available too if you want more grunt. Comfy enough to ride all day long and not as extreme or compact as the current range of 600cc sports bikes. Shouldn't cost much to insure either.