The following are all three-way center channels on the market currently, where the tweeter and midrange are positioned horizontally. I've made and used this list to make my own purchase decisions. The * indicates my recommended choices.
Asperion Intimus 5C Center $280 (not recommended)
Aperion Intimus 5T-DB Hybrid HD Speaker System Measurements | Home Theater
* (5) Infinity Primus PC351 $200 (no anechoic data available)
JBL ES25C $350 (not recommended)
http://www.hometheater.com/content/jbl-es20-speaker-system-ht-labs-measures
* (5) Jamo D 500 LCR $350 (recommended, THX Select 2 certified, no anechoic data needed)
Paradigm Center 1 $380 (no anechoic data available)
NHT Twoc $400 (no anechoic data, but not recommended dues to ThreeC's performance below)
JBL LC1 $400 (no anechoic data available)
* (6) Revel C12 $500 (fantastic)
http://www.hometheater.com/content/revel-concerta-f12-surround-sound-speaker-system-measurements
NHT ThreeC $500 (not recommended)
http://www.hometheater.com/content/nht-classic-four-surround-sound-speaker-system-measurements
JBL LC2 $500 (no anechoic data available)
* (6) Jamo D 600 LCR $600 (recommended, THX Select 2 certified, no anechoic data needed)
Paradigm SE Center $600 (no anechoic data)
Paradigm Center 3 $600 (not recommended)
Test Report: Paradigm Monitor Series 7 Speaker System | Sound and Vision Magazine
* (5) Energy RCLCR $300 (mildly recommended)
http://www.hometheater.com/content/energy-reference-connoisseur-rc-70-surround-speaker-system-measurements
Asperion Verus Grand Center $700 (not recommended)
http://www.hometheater.com/content/aperion-verus-grand-speaker-system-ht-labs-measures and
Aperion Verus Grand Center Overview and Measurements — Reviews and News from Audioholics
* (5) MK Sound S-150THX $750 (recommended, THX Select 2 certified, no anechoic data needed)
* (5) Polk Audio LSiM704c $680 (no anechoic data available)
Paradigm Studio CC-490 $850 (no anechoic data vailable)
* (5) Revel C32 $1800 (recommended)
http://www.hometheater.com/content/revel-performa-surround-speaker-system-measurements
* (6) Revel C52 $2500 (recommended)
http://www.hometheater.com/content/revel-performa-f52-speaker-system-measurements
Revel Voice2 $8000 (not recommended due to price)
http://www.hometheater.com/content/revel-ultima2-studio2-surround-speaker-system-measurements
PSB Synchrony One C $2100 (not recommended)
PSB Synchrony One Speaker System Measurements | Home Theater
Sonus Faber Cremona M Center $4500 (no anechoic data available)
B&W HTM2 Diamond $5000 (no anechoic data available)
B&W CM Centre 2 $1500 (not recommended)
B&W CM9 Speaker System HT Labs Measures | Home Theater
Focal Viva Utopia $12,500 (not recommended due to price) (no anechoic data available)
Focal Electra CC 1008 Be $3500 (mildly recommended)
Focal Electra 1028 Be Speaker System HT Labs Measures | Home Theater
Audio Physic Orea $3700 (no anechoic data available)
Paradigm Signature C1 $1600 (no anechoic data available)
Paradigm Signature C3 $2700 (not recommended)
Paradigm Signature surround speaker system Measurements | Home Theater
Paradigm Signature C5 $4500 (no anechoic data available)
Paradigm Studio CC-590 $1300 (no anechoic data available)
Paradigm Studio CC-690 $1700 (no anechoic data available)
Monitor Audio GXC350 $1700 (no anechoic data available)
Monitor Audio PLC350 $4800 (not recommended)
Monitor Audio Platinum Surround Speaker System Measurements | Home Theater
* (6) Snell CR 70 $1750 (no anechoic data available)
* (6) Atlantic Technology 8200e C $2000 (recommended, THX Ultra 2 certified, no anechoic data needed)
* (6) Polk Audio LSiM706C $1200 (recommended)
Polk LSiM707 Surround Speaker System HT Labs Measures | Home Theater
Selah Sardonyx Center $1200 (no anechoic data available)