A goliath warden is, to date, my favorite character in 4e. I really wish there was a straight answer to your question, a single class that captures the essence of the warden, but 3.5 did not do defenders much at all, and no class really matches the warden. That said, we can get close, particularly if we do use a little bit of a second class.
Goliath Barbarian (Mountain Rage, Lion Spiritual Totem, Wolf Totem) 2/Druid (Shapeshift) 17
Shapeshifter druid is probably the closest you’ll get to the warden. Druid, of course, is a core class, and the shapeshift variant is in Player’s Handbook II. However, since druid is fairly caster-y, we sprinkle on just a touch of barbarian to give more physical presence.
Ultimately, not multiclassing will make you very much stronger – the druid is an extremely powerful class. You can just go with straight druid. For that matter, the shapeshifting variant weakens you; Wild Shape is better and it allows you to take the Natural Spell feat. But the couple of levels of barbarian does two things for you, and does them dramatically:
They improve the power and presence of your shapeshifted form, making that form much more desirable.
They slow your spellcasting, making not shapeshifting and just standing back and casting spells less attractive
These two points are key, to me, for turning a druid into a warden. Without the barbarian levels, as much as you could be a physical powerhouse, you’d be far better off not going into melee and just relying on spells. To turn the druid into a spellcaster who happens to be physically strong, into a real physical presence on the battlefield, the barbarian levels are not to be missed.
When you shapeshift, you gain generic bonuses based on the type of thing you become. There are options like “bird form” which grants flight, “predator” form which grants claws and strength, “natural avenger” form which grants huge reach in the form of vines and the like. The bonuses are decent but nothing amazing. You are recommended to determine, based on your character’s native environment or the environment you find yourself in, to find appropriate appearances for these forms, but that is largely up to you (and does not affect the bonuses you gain). This is important because the warden had a very elemental theme; the shapeshift druid tends to focus on more plant and animal themed forms, but this all very customizable as it is just appearance.
Meanwhile, the druid has powerful battlefield control spells. The warden really specialized in controlling nearby areas, but the druid excels at all forms of battlefield control. At the same time, however, the druid is less able to control the battlefield while mixing things up in melee. Worse, you cannot cast spells while shapeshifting. So it is far from a perfect match, but it is probably the best that 3.5 can do.
Goliath Barbarian with Mountain Rage
I recommend trying to find ways to improve your physical presence on the battlefield. You mentioned the goliath race; that is found in 3.5 in Races of Stone, and it has a very nice option for the barbarian’s Rage, called Mountain Rage. Normally, a druid would hate to multiclass into barbarian, but for your character I think it will work quite well. With it, you become Large during the Mountain Rage, and thus get to threaten a larger area (all reach in 3.5 is threatening reach). You cannot cast spells while raging, but you cannot cast spells while shapeshifted, either, so that mostly works out.
Note that druid also has special goliath “racial substitution levels” in Races of Stone; they’re not compatible with shapeshifter, and mostly not very good anyway. I recommend ignoring them.
Feats, including Improved Trip from Wolf Totem Barbarian
You can also enhance your reach with Aberration Blood and Inhuman Reach from Lords of Madness, and/or Willing Deformity and Deformity: Tall from Heroes of Horror. These are very expensive, particularly since you really want Extra Rage from Complete Warrior first, but they can be impressive. For someone with great reach who wants to control the battlefield, Improved Trip is excellent, and you can get that as a bonus feat, without needing Combat Expertise, from a 2nd level of barbarian with the wolf totem.
On Totems: Lion Spiritual Totem
While on the subject of barbarian totems, there are actually two classes of totem: Unearthed Arcana’s totems, which represent your barbarian tribe, and Complete Champion’s spiritual totems, which represent your own personal spiritual inspiration. For spiritual totem, the lion option is fantastic, granting Pounce at 1st level.
So I recommend something like this:
Goliath Barbarian 2/Druid 17 with the Mountain Rage and Shapeshift variants, with feats Extra Rage (1st), Improved Trip (bonus at Barbarian 2), Aberration Blood (3rd), Inhuman Reach (6th). Willing Deformity and Deformity: Tall at 9th and 12th if you want. Feel free to take Extra Rage more if you find yourself running out of it too much.
Your tactics will involve throwing down some battlefield control spell(s), and then raging and shapeshifting, and pouncing on some poor fool and lashing out all around you.