I have done several things including faucet washers, SS washers, electrical tape, glass and pillar bedding, hanger bars, and foil tape. I have had the best luck with the bedding and hanger bars, but either the barrel/forearm has to be setup for them (hanger bars), or can be a mess and may only work with the barrel (glass bedding). Pachmayr has a hanger bar type method that works with their forearm on Contender pistols. I use this on my Super 14 barrels and works well. If you are using Encore rifle barrels, Stratton Custom has hanger bars made for factory contour barrels. They can also inlet a factory forearm to accept them. I have a few factory forearms that I have bedded for the 24" and 26" factory Encore rifle barrel contours. I also plan on doing the same for the new G2 barrels when I get a chance.
On barrels without a hanger bar or bedding, I have been having the best luck with the foil tape (the same as used for duct work). I put it at both forend screw holes, and stack it thick enough for good clearance but enough for the screws to get a good bite. I use strips about ~5/8" wide at each location, and stick them on the forend. I also have the strip go far enough in the forearm channel so that the barrel won't slip left to right. Electrical tape and bedding tape work about the same way as the foil tape. I have just found a preference for the foil tape over electrical lately.
On Contender barrels, a SS washer works well due to the way the dovetails contact the forearm. Just be sure to pick one that will provide proper clearance, not wiggle too much, and still allow good screw contact with the dovetails.