We can't give you any personal recommendations, since no one on the LVA staff indulges in Karaoke (or, at least, none's 'fessing up to it.) Las Vegas has lots of options, however, which we list in our Shows & Nightlife section.
A good number of hotel-casinos offer Karaoke in one of their bars or lounges, especially the locals joints, while a lot of locals bars have a Karaoke night. The China/Korea-town corridor, essentially concentrated on Spring Mountain Road west of Valley View, also offers numerous Asian Karaoke nights in its restaurants, bars, and cafes.
Of the numerous venues we list, we can vouch for Ellis Island having a long-standing and popular Karaoke scene, ditto the Imperial Palace (although we don't know if this was impacted by the move upstairs awhile back).
The fact that Aliante Station, South Point, and Cabo Wabo at the Miracle Mile Shops have all introduced new "rock star"-style Karaoke nights indicates that the scene is still thriving, and the new Gilley's at TI has introduced "Cowpoke Karaoke". If you're in the mood for something a little (or a lot) different, Sapphire gentlemen's club offers stripper Karaoke, while Brando's pub on Industrial Rd. hosts Karaoke XXX with local porn stars every Tuesday. Only in Vegas. There's an LGBT Karaoke scene, too, with weekly nights at Freezone.
A few of the joints in our listings have been rated/reviewed by other readers, so you can check out their recommendations (or warnings); if you do try anywhere out, be sure to leave your feedback for others to read.