My votes would go to the AV123 Onix Ref100, MSRP $800 in Rosewood, and the Dali Vokal 2, MSRP $650, both of which I own. The Dali has an advantage in that the matching Ikon 6 mains are about $1750 MSRP, whereas the matching Ref3 mains are about double that.
I agree with what John_R posted, especially about the response down to 60Hz. Centers with 5.x" drivers in front ported enclosures are often a good compromise, often offering improved midrange performance over 6 1/2" woofer designs while still playing down to 60Hz. Avoid rear ported designs if possible if you are placing the center in furniture.
Some other centers I would consider in addition to those mentioned in previous posts are the NHT Series 3 center, the ACI center, the Usher centers, Salk Sounds HTS ribbon LCRs and forthcoming SongCenter, Tyler Acoustics centers, and Epos centers. The SVS SCS-01 has been well reviewed in the budget category.