SL Third Party Viewers:

[Monna]

Ascent
Ascent provides expanded control for content creators and developers and improves upon basics such as client detection, parcel management, and asset browsing.

Restrained Love
The RLV enhances your experience when you use it in conjunction with RLV-compatible objects, which are able to restrict the user from detaching items, receiving IMs, hearing chat, teleporting etc.
(note from Oz - this is listed last based on the stability of the 2.x version; a 1.x version is also available. The 1.x version would have been ranked second)

Kirstens
A hybrid viewer based on a mixture of snowstorm and other official sources aimed specifically at high end users, film makers and photography.

Emergence
Emergence viewer is ran by a single developer and is part of an effort to provide users with a safe alternative viewer. Emergence is currently a near clone to Phoenix, as they share this goal, and it is advised to use it instead for higher support.

Imprudence
The goal of Imprudence is to improve the user interface and usability of the viewer through community involvement, thoughtful design, modern development methods, and a pro-change atmosphere.

Phoenix
Phoenix Viewer is a Third Party Viewer based from the LL Snowglobe 1.5 code base, created by The Phoenix Viewer Project Inc (non-profit) Devleopment Team. Large feature set and dedicated Support team available 24/7 to help our users with any issue.

Dolphin ViewerThe Dolphin Viewer is a viewer for virtual worlds, based on the official Linden Lab source code, that contains many fixes and enhancements for builders, explorers, sailors, and other vehicle enthusiasts.

[Monna]

Sorry forgot to limit it to one post on the new feed. Oh dear I m going to go hide before Cale gets on and wants to hurt me for this.

[Skegg]

Kirsten is the best of them.

[Govi]

Kirsten is the best of them.

I might agree but for the fact that it crashes in ten seconds or less.


ETA (a month later): Once I found out what my problem was and the solution (go into the program's folder and switch the openjpeg.dll file for the openjpeg(safe).dll file), Kirstens works like a champ: soooo fast with shadows!!! Yay!!

[Monna]

All the main third party viewers have a their own rss feeds and will now automatically update with their own bots.

If you know of one that is not mentioned please let me know.