I agree and recommend the Summitar. Love mine. And second the suggestion of the Russian 50/3.5 Elmar clones. Many are very nicely coated and are very sharp.
Others I'd recommend, especially for B&W work, though not very cheap, is an early uncoated 35/3.5 Elmar. Tends to flare so not for all situations but a very nice unique signature when kept under control. And a 50/1.5 Summarit. Very cool lens and very unique wide open and excellent performance closed down a stop or two.
If you're going to shoot LTM best when you appreciate that all photography is not only about absolute sharpness and strong contrast.