The PHB2 shapeshift variant permits you to shapeshift as a swift action, instead of your animal companion and your wild shape ability. Shapeshift is much like wild shape; but far simpler rules-wise since you gain enhancement bonuses to strength natural armor and natural attacks, and (I believe) resistance bonuses to fortitude save.
Though these bonuses are quite high (esp. the nat. armor bonus, which is roughly equal to your druid level), they're typed, so that most other effects don't stack easily. It's a good option, even if you don't have the (excellent, IMHO) PHB2, since it's so simply you can easily jot it down from a friends, but almost no ancillary rules make use of it - I would ask your DM in advance if he think's it's OK, and if he's willing to try and let most effects which say "wild shape" to also apply to "shapeshift" (such as wild armor, wilding clasps, etc.), and whether he's willing to work with you to allow feats to choose new shapes.
If you need arguments: although the shapeshift is powerful, esp. if you allow most wild shape enhancement effects to help as well (with the explicit exception of natural spell, which doesn't work at all), it's almost certainly no more so than wild shape. Rather, the (significant ) advantage is that it's only a swift action. That costs you a lot of flexibility (no aquatic shapes, no high-speed shapes, no weird extraordinary attacks such as pounce or trip, no ability to pick and choose the most optimal form from any book), and it costs you your animal companion, not to mention natural spell. As a DM, that's what I do. I let people design new shapes as a feat (it's easy to extrapolate the appropriate power from other shapes), but since you "only" gain flexibility and never power, and the druid isn't exactly feat-overloaded anyhow, I don't have a taker yet (though next level is level 9, I think one might take such a feat then). Really, the PHB2 variant is much much better.
The reason to allow wilding clasps and wild armor and other effects is partially because otherwise the shapeshifting druid has very very little of any use to spend his resources on (which is why everyone is mentioning VoP), and because wilding clasps/wild armor are rather expensive, and not really a problem (imho).
Not allowing these features essentially means that either you're going to take VoP (which is... a little lame), or play significantly below your possible power level (which is fine, but I don't like penalizing players for roleplaying choices and choices which simplify gameplay), or you'll choose wildshape.
the PHB2 has a tentacle-growing spell which is probably not bad (3rd level I believe) as a self-enhancing spell.
