Alot of what you need to warm up has to do with training and nutrition. I can get moving fairly quickly without alot of warm-up but there are times, and I think they are related to nutrition and the amount of exercize I'm getting, it will take me a good 10 miles to warm up. The key is to listen to your body and understand what you body needs to perform. You can't and should not ride like everyone else. If you need to warm up, then take the time, it's not worth risking an injury or a bonk to try and hang in with the fast group if you are not ready. One good suggestion was already offered. Do a pre-ride. On club rides (which are generally very fast) I ride to the venue start. The extra 5 miles before the ride gives me a good warm up provided I don't sit around too long before the ride, timing is crucial. Keep moving. In other words, before you start you ride, get on the bike and just ride, around in circles if need be. Get in the habit of pushing yourself alittle more on each ride. If you generally ride pokey for 5 miles, cut that down to 4. 5 on the next ride, etc. Don't overtrain. Too much riding can cause muscle fatique and the need for longer warm-ups. Also watch what you eat. Make sure your body has fuel to burn. Try a GU before you start your ride. Will give you a quick boost. Now if you are really pokey for 5 miles, than somethings going on in your head and you need to break through some notion you have to hold back some effort. My key has always been to push hard when it's easy (ie flats) and take rest when its hard (ie hills). My speed and intensity of the workout varies throughout the ride.

Good luck. Lots of good suggestions.