I would lean towards Combat Expertise. You're hurting for attack bonus already, but if you're not making a melee attack that round, can't hurt to have some AC. Now, I don't know if you can take advantage of expertise without both hands on the weapon, so many the feat Somatic Weaponry from Complete Mage would be helpful. Lets you use somatic spell components even while holding a weapon, but check the text and make sure it doesn't specify arcane spells.

Huge mercurial Full-blade, with monkey grip and these epic gloves that treat your weapon weilding as if you were a large creature. Or just a large one, but definately a full-blade. I think it's in complete warrior maybe?

The Fullblade is in Sword and Fist, but the stats are only listed in the AEG. There seems to be a lot of discussion over whether the fullblade should exist, though. According to WotC's Larger Weapon Damage tables, the Medium Greatsword listed in the PHB should be doing 2d8 damage already, if the Small damage is 1d10. I couldn't find an errata for it, though, so maybe it's just one of WotC's little quirks.

I couldn't find those epic-level gloves you were talking about - we'll be hitting Epic in about 5 levels, and I'd probably want to nab those then.

Doing searches for all this info made me realize how many kids seem to want to play Cloud Strife. I just thought a battle cleric would want a huge iconic weapon. xD

We've got one in my game. I'll check what he used.

If you make him a dwarf, then the sword will be that much bigger compared to the character (and he'll still be medium, so you can use all your same tricks).

I really like this idea, but I already wrapped up four levels making him an Illumian Half-Dragon.

Don't forget teh magic of the Sun Blade for any of these builds.

The sun Blade is treated as a Bastard sword for terms of size, but a short sword for terms of use. Either WEapon Prof/spec/etc apply.

So, a Sun Blade for a Huge character is Large weapon, and can be monkey gripped in one hand.

(Insert debate about whather monkey grip allows you to only use a LArge weapon in one hand, or if it will let you use a Huge weapon in two... If you can do the later, a Gargantuan Sun Blade could be weilded in two hands).

Holy crap. It's too bad that you can't enchant unique weapons further. I was planning on spending most of his starting wealth adding neat little bonuses to this, and the DM's running a house rule that you can add bonuses later on by paying the difference between enhancement costs.

Actually you can already do that without a house rule. See Adding New Abilities in the SRD

http://www.d20srd.org/srd/magicItems/creatingMagicItems.htm

Sun Blade isn't a unique weapon, just a specific one. I'm not sure why you wouldn't be able to enhance it further.