A couple of new invocations I've been considering to broaden those for the Pact of the Chain, since Tome and Blade seem to be pretty well covered.
Channel through the Chain
Prerequisite: 12th level, Pact of the Chain feature
You have learned to channel greater arcane energies through your connection to your familiar. You can now cast any spell through your familiar, rather than just spells with a range of touch. In addition, any time you benefit from a spell, you can choose for your familiar to receive the same benefit.
This opens up some strategies for the battlefield. Get some distance from your familiar, both hide, familiar fires an eldritch blast to draw the enemy's attention, then confuse them when you start flinging spells from a different direction. Also, if you have mage armor, now your familiar has mage armor too. If you have blur or greater invisibility cast on you, now your familiar benefits too. Cure spell cast your way? You familiar heals too.
Share the Load
Prerequisite: 15th level, Pact of the Chain feature
You have imprinted your arcane talents upon your familiar. When you cast a spell that requires concentration, your familiar can concentrate on the spell on your behalf. This concentration can be disrupted as normal if your familiar takes damage or is subject to effects that might otherwise disrupt it. Your familiar makes its own Constitution saving throw to maintain concentration. Once you use this power, you must finish a long rest before you can use it again.
Warlocks don't get many spell slots, so using two spells in an encounter that require concentration may not happen all that often. But still, if you have a warlock that tends to get into the thick of it, you could have the familiar concentrate and then go hide.