No threads in the DSO forum yet - so I thought I'd add one....
Just to mention my own personal fave Deep Sky Object.

NGC-7789, is an open cluster in Cassiopeia.
I'm a big fan of open clusters, love to view them through binocs and telescopes. Cassiopeia is awash with them, and another fave of mine - the double-cluster (ngc869, and ngc 884) is just over the border in Perseus.
To me though, ngc7789 is the real gem - also known as Herschell's spiral cluster.
Unusual thing about this cluster is that under the right conditions, you get the illusion that it has a spiral structure - of course, being an open cluster, it doesn't have a spiral structure - it's just an optical illusion that you get sometimes.
To see the spiral you need just the right balance of aperture (resolving power) and sky quality.
Under a good steady, dark sky, the spiral will appear at around 6" - to 8" aperture - whereas, from the average town, with some light pollution, you'll need 10" - Bad light ollution in a city will mean you need 12" or more.

Not enough aperture, or inadequate sky quality, and you won't resolve enough stars to get the spiral illusion. Too much aperture - you'll resolve too many stars, and the illusion is lost.

Check it out