I'd like to get some input from others who use their shields aggressively to post some of their favorite techniques.
Now I'm not talking about simply bashing people, knocking them over, sticking a punch shield in someone's face, etc. I'm talking about utilizing the shield to augment your attacks without necessarily hurting your defensive capabilities.
For myself, I've found a few tricks that have lead to significant success, but it's not nearly as expansive as I'd like.
Here's a few moves that I currently have in my toolbag (assuming righty vs. righty). Both assume using a strap shield and a weapon-side foot forward stance, rather than the traditional and more defensive shield-side foot forward stance:
1) Throw a quick mid-level shot to your opponent's shield side. If he moves his shield over even a few inches in reaction to the shot, you step toward him and do a quick and tight left hook with the side of your shield to catch right behind the edge of his shield. You then pull your shield back toward your chest, pulling your opponent's shield away from his body, while at the same time doing a mid-to-high slot into his now exposed chest/stomach. If your opponent doesn't move his shield, make a more exaggerated feint on his shield side to try to create that opening. The result of this move should be a very quick shot/feint-shield hook-slot that leaves your opponent not only dead but demoralized because you ripped his shield away from his body with your arm strength.
2) Start from an exaggerated triangle defense, with your shield angled on the left and the side edge pointing more toward your opponent than usual. Your sword should be angled the same way on your right side, ready to block any crossover attempt. Feint a quick crossover, and if your opponent rolls his shield across his body in expectation to block your crossover, you step in and punch the edge of your shield into the side of his shield, aiming toward his weapon-hand armpit. This exposes the shield side of his body to a good wrap shot. If executed properly, you can twist the crossover feint right into the wrap shot without interruption, with your shield punch happening right in between the two attacks. If you hit hard and fast enough with your shield, you'll not only move his shield (since he was doing a crossover block anyway, this uses his momentum against him), but also trap his weapon-arm with his own shield.
3) This has been met with questions about safety, but I feel that if my shield edge is padded sufficiently then there's no problem. Basically you use this anytime someone tries to do a wide wrapshot to your shield side and you can get the jump on their timing. As soon as they begin their shot, step in and punch with your shield edge into their elbow socket/bicep/armpit/shoulder. This stops their shot dead in its tracks, usually knocks them back a step, and you can get in close and kill them.
As you may have noticed, these are all moves based on the assumption of your opponent's move. As a result they usually work wonders on beginners and intermediate fighters, but have to be used carefully against advanced fighters.
Check out these Hammaborg Viking Shield videos. Not all of it translates, but a surprising amount might.
http://www.youtube.com/watch?v=XWSTx0tZHCUhttp://www.youtube.com/watch?v=R8SRaa33otU&feature=relatedhttp://www.youtube.com/watch?v=zGNBc7ewusQ&feature=relatedhttp://www.youtube.com/watch?v=KXPujfwQJUg&feature=relatedAlso, Magnus addresses this in two of his videos, which are great:
http://www.youtube.com/watch?v=FttIi47k7KE&feature=channelhttp://www.youtube.com/watch?v=bG3heIQtW6c&feature=channel