Hey, it's nice to see all of the referrals to head-fi, which is definitely the best place to ask this sort of question but it's always nice to hear from the Audiogon crowd on headphone-related matters as well.
Depending on your budget, I wholeheartedly agree with the XP-7 recommendation. It's hard to believe that this is a $495 headamp because the soundstaging it produces in awe inspiring - and it's a small portable headamp! I just got mine this past weekend so I'm still in the honeymoon stages with it, but it's leagues ahead of my Creek OBH-11SE or Antique Sound Labs MG Head. My first impressions are that the XP-7 may just compare favorably with well respected headamps in a slightly higher price category such as the David Berning micro ZOTL or the Sugden Headmaster, but I have not done any A/B comparisons yet. Ray Samuels is a great person to work with as well (as is David Berning).
As another suggestion, a head-fi member named Mikhail also produces some excellent tube amps in all price ranges that are a great bang for the buck. The company name is Single Power Audio, and I'm sure he could include balanced inputs in the design if you so require.