If the story of this election is the rise of outside spending, the lesson we at You Report Election 2010 learned is that following the money is next to impossible.

Though big, established political players like the U.S. Chamber of Commerce and the American Federation of State, County, and Municipal Employees poured millions into television ads aiming to sway voters, dozens of new groups — mostly pro-Republican — came onto the scene with ad-buys ranging from small to enormous. And while many of these 501(c)(4) tax-exempt groups flooded the airwaves with attack ads paid for by an undisclosed list of donors, some small groups managed to make an oversized impact by using creativity, new media, and highly controversial messaging to gain the attention of voters and journalists alike.

Through our submission form and the Sunlight Foundation’s Sunlight Campaign Ad Monitor, readers helped us identify some of the best (and worst) independent expenditure ads, mailings, and robocalls around the country.

The vast majority of the independent expenditures we saw attacked Democratic incumbents, while a smaller number went after Republican challengers, took on Republican incumbents, or raised the issue of government spending in general. This comes as no surprise, as independent groups favoring Republicans have outspent those preferring Democrats by almost a two-to-one ratio.

While many groups highlighted the voting record of the candidate they attacked or backed as it related to their own group’s mission, some targeted unrelated vulnerabilities. For instance, we found a single-issue anti-abortion group attacked a candidate’s record on immigration, and a campaign finance reform group accused a Senate candidate of prosecutorial misconduct.