I have heard a lot of pros and cons about both ice and heat after pitching.
In my experiences I have become an ice fan. After I have one of my pitchers throw I like them to warm down with stretching, then I Ice and hang there arm (above the head) while using a TENS unit (when possible).
I feel that the ice helps prevent inflammation, therefore causing less soreness which will speed up the healing/recovery process. Hanging the arm helps rid the body of the inflammation by dispensing it over a larger area of the body through the lymphatic system.
The TENS unit is an electrical stimulator that also aids in the pain control process.
Many pitchers like this combination very much.