One of the great things about astronomy is that your equipment holds most of its value. A $1000 telescope wll be worth $1000 as long as it is in working order. The same with eyepieces.
And eyepieces can become very expensive so that is a good thing. I decided when picking out my telescope that I would get a slightly smaller scope and spend more money on better quality eyepieces. And when it came to eyepieces it is generally agreed that Televue eyepieces are pretty much the best bang for the buck.
My scope came with a 25mm (E-Lux) Celestron eyepiece, so I also picked up an 11mm, 32mm and 40mm Televue Plossl. My plan is to pick up a 24mm Televue Panoptic sometime in the future. The 40mm, 32mm and 24mm eyepieces would then all give the same field of view, just at higher magnifications. I also have a 2.5 and 5x Powermate.
Finally to round out the collection I purchased the focal reducer of the celestron SCT. I highly recommend the focal reducer, it helps a lot on large deep sky objects, and when locating alignment stars.
Being in Calgary, being one of the worse places in the world to observe the sky, I could have done without the powermates. Maximum magnification here on planets is around 200x which can be achieved with a 10mm with my scope. However, the Powermates may come in handy if I ever get interested in looking at the moon in detail, or if I take the scope out of town.
I also purchased a Celstron Omni 4mm eyepiece for collimation. It was somewhere around $50. I just couldn't justify spending more, possibly hundreds for a top quality eyepiece like a Televue Radian or Nagler just for alignment. Perhaps if I get a 4" refractor in the future I will purchase a high power Nagler or other top quality eyepiece but my current scope wouldn't show much detail at that power of magnification.
Filters are one of those many extras which definately are not a must, but do have their places. The purpose of a filter is limit the light coming through to your eye. Different filters limit different things.
I purchased a number of Lumicon filters. Lumicon appeared to be a pretty good brand of filter from my research. There are several types of deep sky filters offered by Lumicon, each limiting different wavelengths of light.
The basic filters are: UHC, OIII, Deep Sky nd Hydrogen Beta. Really after purchasing and using all of these, I would recommend that you really only need one. Either a OIII or UHC filter. Either of these will cover the majority of the observing you will do.
There are also color filters. These are best used when looking at planets. As of yet my planet viewing has been limited to late night Saturn viewing and these color filters I got were somewhat a disappointment. These are Meade brand color filters 82a, 47, 25a, 11. I think my disappointment has more to do with the seeing from Calgary then with the filters themselves.
At any rate, if you are looking to get a filter, I recommend the OIII Lumicon filter. It is a great asset when looking at nebula. Other then that I can't really say filters are worth it.