You started out talking about a greatsword, so I assume you aren't opposed to a two-handed weapon. In that case, falchion is better than elven thinblade. It's 2d4 18-20/*2 slashing, and it's martial.
So, your base attack bonus is either +11 or +12 (depending on the order of your classes) and you have a +2 epic bonus to attack. Skillful (Complete Arcane) is a +2 weapon property that will improve your base attack bonus to +15 (or +17, if your DM takes the fun interpretation) and give you proficiency with whatever type of weapon it's on. If you're going to use that, you should opt for a jovar (Planar Handbook). It deals 2d6 19-20/*2 slashing damage.
You could get a dragonshard pommel stone (The Forge of War) enchanted with skillful and whatever other properties you like. It costs 125% as much as enchanting a weapon, but you can switch it between weapons in slightly over a minute. This would allow you to carry a wide assortment of weapons and change which you use day-to-day.