The Scrum team I'm a member of had never been all that good at raising impediments during the Daily Stand Up - I have no idea why - I think perhaps people got fed up of saying "No impediments" so they stopped saying anything about them at all.
Then one Sprint Retrospective, I noticed that the team was actually very good at identifying problems when doing an exercise like the 4 L's, which was great, but they tended to be recent, (leaving holes from early on), and we'd lost the opportunity to take corrective action quickly, when it could have really benefited the Sprint.
Then it struck me - what if we did a mini retrospective as part of the Daily Stand Up? A "Retro Up" if you like. We obviously needed to keep it short and to the point, so we agreed that everyone had to come to the Stand Up with 2 sticky notes - one detailing something that went well the previous day, and one for something that didn't.
The change was profound - we suddenly got a LOT more (timely) information from the team about how things had been going, plus we got some warm and fuzzy positive feedback too. Once everyone had their say we decided which stickies needed immediate follow up, which could be discarded, and which could be parked until the Sprint Retrospective.
After 3 years of doing Scrum, and trying lots of tweaks to try make the Stand Up more effective, the Retro Up has, by far, had the biggest impact. We just may need to work on the name....