John McCain wants to build 45 new nuclear power plants by the year 2030 in order to meet the country's growing energy needs. According to a Bloomberg analysis, this plan may cost $315 billion, with taxpayers bearing much of the financial risk (potentially $100 billion due to the high default rate on nuclear construction projects).
The cost of constructing nuclear power plants (recently up to $5000 per kilowatt) is also high as compared to large wind farms ($1500-2000 per kW) and solar thermal plants (projected at $3000 per kW by 2015).
In comparison, Obama supports nuclear to some degree, but seems to put the most support on renewable energy whereas McCain seems to only support nuclear and increased oil drilling.
Personally, I far prefer Obama's plan.