Part of what made me choose my element for my elemental adept was the earth elemental as opposed to others that I could have gotten with a focus on Crushing Stone. I'll wait to see what you come up with. 
Here's what the write-up looks like thus far:
Elemental Companion Basics: Use the statistics for an elemental of the appropriate size as found in Chapter 7, but make the following changes:
Level: The character's shaper level.
Bonus HD: Extra eight-sided (d8) Hit Dice, each of which gains a Constitution modifier, as normal. Remember that extra Hit Dice improve the elemental companion's base attack and base save bonuses as appropriate for an elemental. An elemental companion's base attack bonus is the same as that of a cleric or druid of a level equal to the elemental's HD. An elemental companion has good Reflex saves (treat it as a character whose level equals the elemental's HD). An elemental companion gains additional skill points and feats for bonus HD as normal for advancing a monster's Hit Dice (see pages 290-291 of the Monster Manual).
Str/Dex Adj.: Add this value to the elemental companion's Strength or Dexterity score, depending on its type. An earth [ice, magma, ooze,] or water companion adds this value to its Strength score; an air or fire [or smoke] companion adds it to its Dexterity score.
Empathic Link (Su): The elemental adept has an empathic link with his elemental companion out to a distance of 1 mile. The elemental adept cannot see through the companion's eyes, but they can communicate empathically. Note that even intelligent elementals see the world differently from humans, so misunderstandings are always possible.
Because of this empathic link, the elemental adept has the same connection to an item or place that his companion does, just as a master and his familiar (see the Familiars sidebar, page 52 of the Player's Handbook).
Evasion (Ex): If an elemental companion is subjected to an attack that normally allows a Reflex saving throw for half damage, it takes no damage if it makes a successful saving throw.
Death Throes (Ex): When killed, an elemental adept's elemental companion explodes in a burst of elemental energy that deals 1d6 points of damage per Hit Die to anything within 20 feet, with a Reflex save (DC 10 + 1/2 HD + elemental's Constitution modifier) for half damage. An air companion deals slashing damage with this ability, an earth or water companion deals bludgeoning damage, and a fire[, magma, or smoke] companion deals fire damage[, and an ooze companion deals acid damage].
Size Increase (Ex): A 3rd-level elemental adept's companion grows into a Medium elemental of the same kind. When it does so, its statistics change appropriately. An elemental companion never increases in size beyond Medium, regardless of its Hit Dice.
Devotion (Ex): An elemental companion of a 3rd-level elemental adept is so devoted to its master that it gains a +4 morale bonus on Will saves against enchantment spells and effects. This devotion also improves the elemental’s defenses, granting it a dodge bonus to its Armor Class equal to ¼ its master’s shaper level.
5TH LEVEL FEATURE (Ex): The elemental companion of a 5th-level elemental adept ??????????
Elemental Strike (Ex): When the elemental adept reaches 7th level, his magic begins to empower the attacks of his elemental companion. The elemental companion gains an enhancement bonus equal to ¼ its master’s shaper level on attack rolls, and its natural attacks are treated as magic weapons for the purpose of overcoming damage reduction. The companion also deals additional damage with its natural attacks equal to its master's Charisma modifier.
In addition, the elemental's empowered strikes allow its master to more easily pierce the defenses of his foes. If his elemental companion successfully strikes an opponent with a melee attack, the elemental adept gains a +2 bonus on any shaper level checks made to overcome that creature's spell resistance until the beginning of his next turn.
Extra Attack: When the elemental adept reaches 7th level, his elemental companion gains a second attack with its primary attack form.
Advancement (Ex): As an elemental adept increases in level, his elemental companion becomes more powerful. When the elemental adept reaches 9th level, his elemental companion becomes tougher and smarter, gaining +2 Constitution and +2 Intelligence. In addition, an earth [or ice] companion gains a +1 increase to existing natural armor and a [magma, ooze, or] water companion gains +2 Dexterity.
At 15th level, the elemental adept's companion continues to become more powerful, gaining +2 Constitution. In addition, an earth [or ice] companion gains a +2 increase to existing natural armor, and a [magma, ooze, or] water companion gains +4 Dexterity.
When the elemental adept reaches 19th level, his companion gains another +2 Intelligence. In addition, an earth [or ice] companion gain a +2 increase to existing natural armor and a [magma, ooze, or] water companion gains +2 Dexterity.
Damage Reduction (Ex): If the elemental adept is 9th level or higher, his elemental companion gains damage reduction 5/-. When he reaches 19th level, this damage reduction increases to 10/-.
Improved Speed (Ex): All of the elemental companion's speed figures increase by 10 feet when its master reaches 11th level.
Improved Evasion (Ex): When subjected to an attack that normally allows a Reflex save for half damage, the elemental companion of a 13th-level elemental adept takes no damage if it makes a successful saving throw and half damage even if the saving throw fails.
Scry on Companion (Sp): If the elemental adept is 13th level or higher, he may scry on his companion (as if casting the scrying spell) once per day.
Spell Resistance (Ex): If the elemental adept is 17th level or higher, his elemental companion gains spell resistance equal to the elemental adept's level + 5.
So, not
much has changed--I've really just been clarifying things and double-checking so that everything works with the fluid and solid subtypes. The brackets include the information on paraelementals, which won't be in Codex I--but will be updated online.
Incidentally, that undecided 5th-level ability is almost certainly going to be non-element specific. It's much easier to deal with the companions if they get the same benefits. Let's face it, my revised elementals are already different enough--and it's hard to come up with simple ways for them to more fully embody their respective elements. For the same reason, I'm probably going to axe the Elemental Perfection feat. I hope I'll be able to come up with something to replace it...but we can only hope, at this point.
Oh, don't worry, I know about all the different things that you can make a pact with...
Actually, a Slaad pact would be hilarious as hell.
Everyone else gives a thematic set of formulae, while Slaad give you...
Well, did you see my post about UTTER RANDOMNESS? 
Kidding, kidding; though my write-up will have a rather unorthodox way of using Formulae (that's how I've done every single ToB base class I've ever written, and some people think that at least one of them is excellent, so...)
The "unorthodox" way of using formulae makes me twitchy, but I'm not going to reject it until I see it. Mind if I ask which classes you're talking about?
Also, though such things are pretty common in fantasy, let's stay away from pacts with elementals and dragons. Don't want to step on any toes, after all.
