I recently up-dated my 10/22. It now has a Green mountain fluted bbl, Hogue stock, and a Leupold 3-9X40(with Leupold rings and bases). I recently took it out the the range and shot some Winchester ammo through it. It cycles the ammo fine, but my groups aren't any better than when I had the factory orginal bbl. on it. I'm getting around 1" to .75" groups with it off the bench with a Harris BR bipod. Is there a better ammo...or is this really as good as it gets?

You can try several different brands to see what your rifle likes the best.  Federal Gold Medal Match (900) is pretty good.  Eley makes several different loads, as well as Lapua, and RWS.  Should be able to find one out of the above mentioned that will do the job you want done.  Don't be scared of the price tag though, you get what you pay for.  That said you may find a cheap domestic, that will fit the bill as well.  YMMV
Good Luck!

I agree with CIB, I have quite a few different 22 rifles that I shoot off the bench and they all have different preferences in ammo.
Some that have been "better than average" in multiple rifles are Fed Lightnings, Wolf MT (When you can find it) Eley Subsonic plus HP and SK Match (Wolf MT in a different box if Champion Shooters Supply is to be believed)
Most people I know that have used Green Mountain barrels have been impressed with the accuracy.
A lot of Rimfire BR shooters I know seem to have good luck with Winchester Dynapoints though personally nothing I own seems to like them.
Hope that helps,
Paul
Edited to add: What distance are you shooting at? and does your scope have an adjustable objective? Scope parrallax(sp?) could be part of the problem.
Paul

I had good luck in my factory stock 10/22 with Winchester Dynapoints. Different guns like different ammo.

This rifle happened to really like the dynapoints, I did not measure groups at 50 yards I have not tried them in any of my other rimfires yet

Check out this web site http://rimfirecentral.com/forums/showthread.php?s=&threadid=40223

Dan