I'm partial to Keith Laumer and he has quite some great time stories. The best of them is probably The Dinosaur Beach, available in Odyssey collection:
http://www.webscription.net/p-301-odyssey.aspx
The Lighter Side has several of more light-hearted stories. I especially liked The Great Time Machine Hoax.
http://www.webscription.net/p-249-the-lighter-side.aspx
Then there's the Imperium series:
http://baencd.thefifthimperium.com/1...arCD/Imperium/