One of the reasons I wrote up the stats for the Wild Cat for Fiery Dragon was to fill a gap in the feline size progression. Now you can go from Tiny (cat) -> Small (wild cat/lynx) -> Medium (cheetah/leopard) -> Large (lion/tiger).
I also did the same for the Dog (just go to
www.fierydragon.com and click on the Dragon's Breath logo and then choose the article "Good Boy!" from the list). I divided the Dog in Tiny (pug to poodle to daschhound in size), Small (beagle to retriever) and Medium (german shepherd, mastiff, great dane).
I might do the same for hunting birds, from Tiny (Hawk) to Small (Falcon) to Medium (Eagle).
Edit: Here's a Medium Tiger for your druid:
Juvenile Tiger: Medium Animal; HD 6d8+6 (hp 33); Init +3; Spd 40 ft; AC 14; BAB/Grap +4/+6; Atk Claw +6 (1d6+2); Full Atk 2 claws +6 (1d6+2) and bite +1 (1d8+1); Space 5 ft.; SA Improved grab, pounce, rake 1d6+1; SQ ll-vision, scent; Saves Fort +6, Ref +8, Will +3; Str 15, Dex 17, Con 13, Int 2, Wis 12, Cha 6; Balance +7, Hide +8*, Listen +3, MS +10, Spot +3, Swim +7; Feats Alertness, INA (bite, claw).
To it, apply the abilities of an animal companion of a 1st-level (druid). When your druid reaches 7th level, do not change the companion abilities (keep as 1st level). Instead, just advance size to Large:
+8 Str, -2 Dex, +4 Con, +2 natural armor, -1 attack/AC, increase damage to 1d8 (claw/rake) and 2d6 (bite) and increase hit points to 45 (accounting for the Con increase to the bonus hp from 6d8+6 to 6d8+12). Size also adds +4 to Grapple and -4 to Hide checks.