My lore bard might do a L2 warlock dip. Looking for ideas
You'll hear a lot about Devil's Sight, and for a human it's a pretty nifty Darkvision replacement, but unless your whole party is already full of heavy obscurement and darkness tricks I find there are better things to do with your invocation + concentration (e.g. Hypnotic Pattern). That is, if there's an Alert Shadow Monk, a Moon Druid using snake or elemental form for Blindsense, and a Skulker Rogue in your party, so that you're not spending your own concentration on Darkness but relying on the Shadow Monk's Darkness, then I'd go for Devil's Sight.
Otherwise, I find it useful to have at least one guy in the party with 600' range and Spell Sniper/Sharpshooter capability so that you're never outranged by hobgoblins/etc., which means you might look into Eldritch Spear. If someone has that covered already then Repelling Blast is my favorite no-concentration way of abusing enemies. Spike Growth + Repelling Blast is an amazing combo (+4d4 damage per hit PLUS making the enemy slog right back through that difficult terrain, taking another 4d4 damage on the way... 8d4 makes Hex's 1d6 look like chump change) and Wall of Fire is similar (+5d8 per hit). An awful lot of crowd control spells like Stinking Cloud get much better if you have an easy way to knock enemies back into them, and with Agonizing Repelling Blast you're not choosing between damage and control, you're getting both at the same time!
Infinite Disguise Self is fun in completely different, non-combat way. Did you ever see X-Men? Yeah, at-will Disguise Self is like being Mystique the Super Spy.
False Life at-will has a good reputation at low levels as being extremely useful. Me, I'd rather just take Inspiring Leader as a feat and benefit the whole party instead, but it's certainly something to consider. Ditto Armor of Shadows for at-will Mage Armor--I wouldn't do it myself, but it's quite popular.
Finally, One With Shadows as written is useless, but at my table I let warlock players use something mechanically identical to the Shadow Monk's Cloak of Shadows (i.e. you can move while cloaked, you just can't take actions) and my players seem to have lots of fun with it. See if there are any invocations like that that your DM is open to rewriting to make them work better.