[Lord Plothos]

If you take TWF, TWD is a good idea. Why not get a free point of AC?
On the whole, TWF isn't a better option than just using a two-handed weapon, IMO. Damage is roughly comparable overall, but you have to enchant two weapons rather than one, and you have to burn feats that could go toward weapon focus, dodge, and the like. I like dodge, btw. Free AC is always good. A pure ranger can't get weapon specialization or anything, so there aren't a huge number of feats that'll enhance his melee beyond ITWF and GTWF. Feats like mobility, spring attack, or even skill focus in tumble can be very useful. Whirlwind can be fun, though it's better with reach weapons.

In short, there are a lot of feats out there that'll help. I don't think I've ever taken toughness with any character. Just about anybody can find something better to spend a feat on. But no feats are so important that you can't live without them. Don't worry about it too much.

Oh, since you said you took TWD (or were considering it) I presume you have a 15 dex. If your dex is significantly higher than your strength (or even just a point, really), you might consider weapon finesse and a rapier for your primary weapon.