I really enjoy the barbell side press.
I've seen lots of definitions of what constitutes a side press, from almost a military press to almost a bent press. I use the form shown in PTTP: Starting position with the elbow back and the upper arm supported by the tensed lat, push yourself away from the weight at the start, but press the weight out with the arm. It ends up being closer to a military press with some body lean than a bent press with dramatic folding under the weight.
Some form points I've found helpful:
--Find the best balance point for your grip. I center the bar over the base of my pinky. If I try center my hand on the bar, the balance will be off and the bar will want to sway all over the place. If I center the base of my pinky on the bar, the balance is very stable; the bar just sits there and doesn't sway at all. I actually find the barbell to be more stable and forgiving than a KB or DB.
--Tightness in the bottom position is a big key. The easiest way to learn this is to LOWER the bar into position for the first rep from overhead. Snatch or jerk the bar overhead and then lower it into position to start the first rep, focusing on pulling the bar down and keeping the lat tight.
--If not starting from the top, it is easier to take the bar out of a rack at shoulder height than to wrestle it into position from the floor. You can load up tension in your starting position, then dip your knees to get under the bar, set your grip, and take the bar out of the rack with your body already tight.
--These methods of getting into the starting position also have the advantage of not putting any stress on your collars; since the bar is never tipped on end, you don't have to worry about collars and plates slipping.
--Compared to a 1-arm military press, the lat is more involved, and there is a more dramatic wedging effect. My 1RM KB MP is 36kg (about 80lbs). But I can do this style of barbell side press with 95lbs for 5 reps and have maxed out at 110lbs for a single.