Quasars
3C 273 is the only quasar visible through a 150-mm telescope. It is located in the Virgo-Coma cluster, south of M61. The distance that separates Earth from 3C 273 is 2.6 billion light-years (redshift 0.158).
Finding the quasar can prove quite difficult, it is located in an area deprived of bright stars and it took me almost 15 minutes to find it. When I observed 3C 273, its magnitude was 12.5 (it varies between 12 and 13). Seen through the telescope you can’t distinguish it from a star.
Supernova Remnants
M1, the Crab Nebula, is a supernova remnant in Taurus. At 36x it is very spectacular, one of the very few deep sky objects that when seen through the eyepiece looks almost exactly like when seen on a photograph. The light is evenly spread and the elongated shape is easily visible.
You can find NGC 6960 (Lace-Work Nebula, part of Veil Nebula) around the fourth magnitude star 52 Cygni.
The nebula is very difficult in less than perfect skies, but visible with a 114-mm telescope from a dark location. Use averted vision, and keep 52 Cygni just out of the field.
A UHC or OIII filter can really improve the visibility of the nebula, it allows much more contrast and detail to be seen.
Nearby stars
Lalande 21185 is the brightest red dwarf visible from the northern hemisphere and the fourth system closest to Sun after Alpha Centauri 3, Barnard’s Star, and Wolf 359. The star is located only about 8.3 light-years away in the constellation Ursa Major. I found it using Sky Atlas 2000, it was easily visible with the 114-mm telescope.
Barnard’s Star is the closest star system to our own visible from the northern hemisphere, located at only 5.9 light-years from us. You can find it a little to the west of Beta Ophiuchi.
It is difficult to find, but with a little patience you will succeed. Sky Atlas 2000 has a special chart for finding this star.
Other nearby stars I’ve seen are Groombridge 1618 (Sky Atlas chart 2), Groombridge 1830 (Sky Atlas chart 6) and 16 Cygni (Sky Atlas chart 9).
Double stars and asterisms
M40 is a faint double star in Ursa Major, which found its way into Charles Messier’s famous catalog by mistake. It is easily split into components at 36x, both stars are slightly red.
M73 is an asterism composed of four stars of 10th to 12th magnitude, situated in the very western part of constellation Aquarius. It is difficult to see at 53x, and the stars are grouped in the form of a trapezium. Even at 120x the asterism is difficult to split into component stars.
The three brighter stars (magnitude 10) are somehow easier to see, but the forth (magnitude 12) is difficult, even when using averted vision.