Another Suggestion... I know, I can't believe it either

Still sick and still leafing through my books in my spare time, came across this simple little Invocation for warlocks in the Drow of the Underdark book that'd give 'em another polymorph option.

Spider-Shape
Invocation Level: Lesser
Spell-Level Equivalent: 3rd

You can transform yourself into the form of a fiendish monstrous spider for a number of hours equal to your caster level, or until you choose to end it.

In PnP, you can choose it's size, starting off with Medium and Small, but getting Large at 8th level, Tiny at 11th, Huge at 15th, and finally Gargantuan at 20th. I figure you could work it in the system as a passive bonus to the stats granted in the forms when you hit the 8th, 15th, and 20th Caster Levels.

I'm not really looking to add more ways to polymorph. It's enough of a headache as is.