These folks are the "quiet company" for web and desktop players for Flash and Silverlight. But their free products just keep getting better. http://www.longtailvideo.com/players/
I just visited the JWPlayer website and see that this new version implements "bitrate switching" - a really nifty feature that allows you to reference several source videos with varying bitrates/sizes and the player will auto-magically switch the quality of the clip based on the user's connection speed. click here
...Jerry
Edit: upon further reading, it looks like JWPlayer V4 had implemented "bit switching" - it's still a good feature. I'm experimenting with the configuration.
Okay, upon further research, I think I became prematurely excited. It looks like, in order to implement "bit switching", there are some constraints.
1) For HTTP Streaming your Hosting Service must install some specialized software (e.g. H264 Streaming Module for IIS), or
2) For RTMP(Real Time Messaging Protocol) Streaming, your video(s) must be located on an RTMP Server.
If anyone reads the documentation differently, please post a reply.
I love JW Player but I wish they would stop supporting YouTube videos. That allows sites and apps (e.g. most of those Facebook YouTube apps) to bypass YouTube ads and links and overlay their own ads.