The underlying idea (aside from making interesting new potions) is to take all that low-level crap you either sell, store in a chest to never look at it again, or just throw away and turn it into something useful instead. Clean up your inventory by combining potions! Only works for vanilla potions, not user-generated ones. Comes in two flavors - basic and extended.

Requested on the nexus forums, and I decided to run with it.

The basic mod

Will take 2 equal potions of "restore (stamina/health/magicka)" and create a higher-level potion. Created at a cookpot, under the misc section. Only the potions you can actually mix with the items in your inventory will be shown in the list. Right now the scheme is

01+01=02, 01+03=04, 02+02=04, 03+03=05, 04+04+04=06, 05+05=06

Based on the restoration levels found in vanilla:
01=25pts, 02=50pts, 03=75pts, 04=100pts, 05=150pts, 06=9999pts (full)

New in v1.2: You can now also combine the fortify health/stamina/magicka and the recovery rate potions for same, but this will happen using the same simple formula, so for min/maxers this may not be a great solution (as these potions typically have durations and/or small increments and I think they stack). Purely included for inventory de-clutter types. Combine away!

The extended mod

This starts with the basic mod and has all the same features but adds new potions. This is where further development will take place, the basic will remain as-is. The idea is to combine different potions and gain different effects. Sometimes complementary (will be stronger than the original potion), sometimes conflicting (will be stronger, but have negative side effects), sometimes just odd. None of these potions will be sold, they can only be mixed.

UPDATE FOR 1.2: The potions added now require alchemy skill perks appropriate to their level and type, so for, say, the distilled frostbite poison you will have to have both the poisoner perk and alchemist perk - the more distilled the poison, the higher the perk level required. Not sure if this is going to be a popular change, but it seemed fair.

Warning: the extended mod is basically a playground for me to toy with new combinations and effects. While I do my best to stick to sane values, there is the possibility that one or more are over- or underpowered. Let me know if you think that happens. I'm open to suggestions (but reserve the right to ignore them if I so choose), so if you have requests or interesting combination ideas, please leave them as a comment .

New potions added to v1.2 on 2012/11/22 (extended version only):

Potion of Quickshot 01-04
Turn into an arrow-spitting menace for a while! Stacks with the quickshot perk. (beta test, please provide feedback. No negative effects in place yet). Requires additional ingredients beside potion(s) - which ones? That's for you to find out!

Poison of Polymorph chicken/rabbit
Turn your enemies into chickens or rabbits for a short time or until hit! (beta test, please provide feedback). Requires additional ingredients beside potion(s) - which ones? That's for you to find out!

New potions added to v1.1 on 2012/11/21 (extended version only):

Craftsman's Potion 01-04
Combine blacksmith's potions for extended duration and higher magnitude. Complementary.

Potion of Vitality 01-04
Combine fortify health + healing rate for extended duration and higher magnitude. Complementary.

Concentrated Frostbite Venom 01-03
Distill up to three times for a more potent poison.

Potion of Resistance 01-04
Combines all resistance potions for better resistance for each but with stamina damage over time. Conflicting.

Potion of Packrat 01-05
Increases carry weight and stamina. Complementary.

Potion of Doom 01-04
Increases magicka regeneration and increases destruction skill, at the cost of slow health loss. Conflicting.

MOAR to come ;)