My DM is letting me have a swarm of wasps as a 1st level animal companion.  Here are the stats we came up with.  It's basically a swarm of spiders that can fly, and therefore some of their other abilities have been removed.
They're pretty nice, but I'm not sure they're nicer than a wolf.  The - Int means they only know 1 trick ("attack").  We're ruling that they swarm around me, but don't sting me.  I must occupy part of their 10' space.  They're also nice because I can "put them away" underneath my robes whenever we hit the town.
The Scratch
WASP SWARM
Diminutive Vermin (Swarm)
Hit Dice: 2d8 (9 hp)
Initiative: +3
Speed: 10 ft. (4 squares), fly 30 ft.
Armor Class: 17 (+4 size, +3 Dex), touch 17, flat-footed 14
Base Attack/Grapple: +1/—
Attack: Swarm (1d6)
Full Attack: Swarm (1d6)
Space/Reach: 10 ft./0 ft.
Special Attacks: Distraction
Special Qualities: Immune to weapon damage, swarm traits, vermin traits
Saves: Fort +3, Ref +3, Will +0
Abilities: Str 1, Dex 17, Con 10, Int —, Wis 10, Cha 2
Skills: Climb +11, Perceive +4, Sneak +7
Challenge Rating: 1
Alignment: Neutral
Combat
A wasp swarm seeks to surround and attack any living prey it encounters. A swarm deals 1d6 points of damage to any creature whose space it occupies at the end of its move.
Distraction (Ex): Any living creature that begins its turn with a wasp swarm in its space must succeed on a DC 11 Fortitude save or be nauseated for 1 round. The save DC is Constitution-based.
Skills: A wasp swarm has a +4 racial bonus on Sneak checks and a +8 racial bonus on Climb checks. It uses its Dexterity modifier instead of its Strength modifier for Climb checks. It can always choose to take 10 on a Climb check, even if rushed or threatened.
Spider