So it occurred to me that there are quite a few different grenade ‘features’ some of which sort of cancel each other out (sticky impact) and some that enhance each other (divider MIRV), for example, and I started making notes about all the features I could find. There’s a lot! Some (all?) of these can be included in a grenade at least twice, though they appear to have diminishing returns. Two Rain modifiers makes four child grenades, not six, for example.
Delivery systems:
- Lobbed: this is a normal, arced toss.
- Longbow: grenade teleports straight to where you’re aiming.
- Homing: grenade floats around until it detects an enemy, then pursues it.
- Rubberized: grenade is pitched a short distance in front of you where it detonates with a basic explosion (of its element). It will continue bouncing forward and off objects/enemies like this for four bounces, doing extra damage over more range per each bounce. On the fifth bounce, it fires its actual detonation system. Rubberized is a rough delivery mechanism, but you do get (let’s assume 10% per bounce) up to 50% more damage and range if you can manage to get that last bounce on target.
Trigger systems: - Impact: grenade will detonate immediately upon contact with anything (enemy or surface)
- Exploder: grenade will detonate immediately upon contact with an enemy only (if it hits the ground, it’ll just flop there until the fuse expires).
- Sticky: grenade sticks to surfaces and/or enemy. If it sticks to an enemy, you get bonus damage. If it sticks to a surface, it turns into a prox mine.
Detonation systems - Artillery: grenade bounces around spraying bullets (an old bouncing betty)
- Bouncy: bounces up to 3 times with detonations on each bounce. The difference between this and a Rubberized delivery is that these bounces start at the point of impact based on any delivery mechanism, and don’t have increasing damage per bounce (where rubberized do, and can only start right in front of you).
- Jumping: upon detonation, grenade shoots a copy of itself upward, where it falls back down for a second detonation with 10% more damage.
- Rain: upon detonation, grenade shoots a copy of itself upward, where it floats for a moment and fires three grenades down. The difference between this and Jumping is that the three that come down are spread out and don’t get the 10% modifier.
- MIRV: grenades pop into three. Unlike Rain, they pop wide and don’t jump up at all.
- Mini MIRV: like a regular MIRV, but the three child grenades are themselves MIRVs that drop three child grenades each.
- Singularity: creates a vortex that will try to rise upwards briefly while pulling enemies (and barrels because that’s awesome) towards it before exploding.
- Chiller: cryo AoE (sprays cryo damage for a few moments)
- Corrupter: corrosive AoE (sprays corrosive damage for a few moments)
- Blight: radiation AoE (sprays radiation damage for a few moments)
- Flamer: fire AoE (sprays fire damage for a few moments)
- Tesla: shock AoE (sprays shock damage for a few moments)
Damage Systems - Roider: 20% more damage in general.
- Link: 15% extra damage for every enemy damaged by grenade effects.
- Large: 20% larger explosion radius
- Nuke: consumes 2 grenades for the throw with 50% more damage output.
- Divider: two grenades appear for the one thrown. They’ll be staggered a little, and won’t detonate at the exact same moment (like maybe a tenth of a second apart).
Enhancement systems - Generator: heals shields
- Transfusion: heals health
- Force: strong knockback
- Money: enemies drop cash when damaged
- Elemental Damage: 20% more elemental damage and 85% chance
- (Special Red-Text: Funguy, Hex, Whispering Ice, for example): these each have effects unique to their respective grenades, and all use the same line item icon.
So what’s a great combination you’ve found (that’s not a Unique)? The more I look in the vending machines, the more possibilities seem fetching indeed. Do let me know if I’m missing something (or if you figure out what the fire and shock AoE prefixes are).
(edit - note to self: figure out/add mini-MIRV) 
edit - added fire and shock AoE names
