SpeedBit Video Accelerator reduces buffering problems when viewing standard and HQ videos on YouTube and many other sites. The program automatically detects when you are viewing a video from one of the supported sites and automatically accelerates the transfer by using multiple parallel connections, thereby allowing for significantly improved download speeds and video playback.
You are probably more likely to run into buffer issues when you are watching HD quality videos, but unfortunately these are not supported in the free version. Nonetheless, if you experience frequent buffer issues while watching standard quality videos online, give this program a try.
SpeedBit Video Accelerator can accelerate standard quality video for more than 160 sites (YouTube, Yahoo, DailyMotion etc.) and the optional Premium version also supports HD videos for a portion of them.