Assuming you can make out the telescopes, from left to right we have the United Kingdom Infrared Telescope (UKIRT), the Caltech Submillimeter Observatory (CSO), the James Clerk Maxwell Telescope (JCMT), the Submillimeter Array (SMA), Subaru, Keck I & II, NASA's Infrared Telescope Facility (IRTF), the Canada-France-Hawaiʻi Telescope (CFHT), and finally Gemini North on the right. There are, in fact, only two telescopes on the summit that are not in this picture: the UH 2.2-meter telescope (directly behind me while taking this picture) and Hōkū Keʻa, the new UH 0.9-meter telescope that was finally installed this semester (and just achieved first light on the 17th, I heard. It's hidden behind UKIRT in this picture).
(If anyone is having trouble identifying the telescopes, I'd be happy to create a labeled version for you. Just let me know.)
Addendum: I just now realized that while there are technically no more telescopes on the summit of Mauna Kea than were mentioned in the preceding paragraph, there is one more close to the summit. That one would be the Very Large Baseline Array telescope, which is pictured two posts prior to this one, on the entry for June 24.