Shield lob is kind of your only real choice if you're going to try to gather adds from a distance, at a level where you don't have access to Provoke. Once you have Provoke, you'd just use that instead and then a shield lob to make sure whoever it's hitting doesn't just reel it right back to them.
Like a lot of other people have said, Flash is your go-to for trash pulls as GLA/PLD. If you don't use at least two Flashes per pull as you rotate through targets with Savage Blade (and eventually Rage of Halone), you're going to be in for a Bad Time because you just won't have enough threat on stuff you're not directly attacking. Also, if you're tabbing through targets and see something about to peel away from you, hit it with Shield Bash so it's stunned as it turns red--this gives you 3 or 6 seconds to get some kind of enmity on it so it doesn't run away. If you get the timing right, nobody notices you let one slip away because it never leaves your side and you look like the Best Tank Ever.