I've been an amateur astronomer for 26 years. I am a "casual but experienced visual observer." I favor the aethetic over the scientific, so my opinions are colored by this bias.
In my years of casual observing I've amassed a decent collection of affordable eyepieces, and have decided to share my notes for each with you. Several of them are no longer manufactured, but do come up from time to time second hand, so I believe this evaluation has present-day relevance.
6mm University Optics Plossl - circa 1983. Multi-coated. Made in Japan. No longer sold. Good high power ocular with too short eye relief and uncharacteristically (for a Plossl) small AFOV. There are better choices today, but back then this was an affordable alternative to very expensive Clave Plossls.
7.5mm Orion (Vixen) Lanthanum - circa 1999. Nice moderate high power eyepiece with great 20mm eye relief on a decent 50* FOV package. No longer sold. Compared to the aus Jena Ortho, the Edmund RKEs, Celestron Ultima or even Celestron Plossl, the Lanthanum is a little "mushy" and doesn't measure up in fine detail studies. That said, this is a good eyepiece for sharing your scope with novices. The long eye relief makes it easy for a beginner to get a good comfortable view.
8mm Edmund RKE - new. Made by Edmund Industrial Optics in the USA. Excellent planetary and lunar eyepiece. Expensive now at $57. Also, some sleaking noted on coatings on this new unit. Not as good in this regard as the "vintage" RKEs in the collection, but still one of my favorite oculars for higher power use.
9mm Stellarvue Plossl - circa 2000. This one looks coated rather than multi-coated. These are similar to Orion's Sirius Plossls. Reasonable value for the money (at around $30-40) but not as good as Japanese Plossls commonly available second hand such as the Vixen's Celestron used to re-brand and ship with its scopes.
9mm Orion Ultrascan - circa 1990. Fully-multi-coated. Made in Japan. No longer made. 77* AFOV (!) Hawked as a cheaper alternative to Meade UWAs and TV Naglers. These are decent eyepieces with good on-axis performance, but lose something at the edge of field. They also have very short eye relief. Kind of like peeking through a small knot hole in a fence.
10mm aus Jena Abbe Orthoscopic (0.965" with adapter for 1.25") - circa 1987. Like a good spy novel, I wrangled this eyepiece from behind the iron curtain back in the Cold War days. "aus Jena" was the export brand of the East German branch of the Carl Zeiss company. This is a coated (not multi-coated) ocular. It looks funny and amateurish. It is a great eyepiece. One of my best. Highly recommended if you can find one second hand. You can get true Zeiss Orthos now, but they are in the near $200 range.
12mm Edmund RKE - Circa 1996. Well made in the USA by then Edmund Scientific Company. Nice coatings. Great performer optically. Was in the $40 back then. Still made, though possibly not to the same standards, but it's almost $60 now. Look for these used if you can find them. If your intended use isn't hampered by the realtively narrow 45* AFOV, highly recommended.
15mm Celestron Ultima Wide Angle - circa 1995. No longer made, but possibly superceded by Celestron's Axiom line. Nice, fully multi-coated ocular with AFOV in the 70* range. Eye relief is a little short, but otherwise a great performer in a very useful focal length.
15mm Parks Gold Series Plossl - circa 2000. Not really a Plossl, which is a 4-element beast, but rather a modified Plossl featuring 5 elements. Similar to Orion's Ultrascopics and Celestron's Ultimas (not the Axiom of older Wide Angle Ultimas), but different coatings. When you look at an Ultrascopic, Gold Series and Ultima side by side you see that the Ultima has a heavy red-green coating, the Orion has a deep blue-green coating and the Parks has a paler violet-blue coating. Of these three based on star party use I like the Ultima, then the Parks and finally the Orion.
20mm Meade Research Grade Erfle - Circa 1983. No longer made. 65* AFOV. Multi-coated and made in Japan. I LOVE this eyepiece! It is well made, very light weight (all aluminum barrel) and packs a wonderful visual punch in a compact package. Good images, with characteristic Erfle edge distortion in fast scopes, but otherwise perfect. If you can find one second hand, buy it by all means.
21.5mm Edmund RKE - Circa 1996. See notes from the 12mm model. Nice eye relief and Barlows very well.
26mm Celestron Plossl - circa 1995. Made in Japan by Vixen. Multi-coated. Sharp flat images with 50* AFOV. Nice but inferior in contrast to newer Ultimas. This is the eyepiece Celestron used to distribute with its re-branded Vixen refractors. It is not the same as the Chinese Plossls they now bundle with new scopes.
32mm Stellarvue Deluxe Plossl - circa 2000. See comments for the 9mm, except For a low power object locating eyepiece, where ultimate contrast isn't the main issue, this one is a really good value.
35mm Celestron Ultima - circa 1998. My favorite low power eyepiece. Fully multi-coated. Sharp edge to edge. No internal reflections. A little bit of blackout if your head isn't in the correct position, but once you get the position down this is among the best I've ever used.
50mm Parks Plossl (2") - Circa 2001. More of a black out problem than the 35mm Ultima, but produces wonderful very low power, very wide true field views. Beautiful on extended regions like the Sagittarius Star Cloud in the late Summer Milky Way. In my 3" f9.4 achromat this porduces about 15x. It turns my scope into a 15x80 monocular with a 2+ * true FOV. Worth considering if you have a scope with a 2" focuser.
That's it. My entire eyepiece case in a nutshell. Of these here are the ones I couldn't live without:
8mm RKE, 10mm aus Jena, 12mm RKE, 20mm RG Er, 35mm Ultima.
If you find any of them second hand, jump on them. Amazing value for the money.