My biggest concern from independants is game balance. As long as it isnt too powerful, I'll consider using it, especially if a player of mine asks me to look it over.
I did examine a few Mongoose books, but saw nothing warranting a purchase as of yet.
My favorite indeps in order are...
Necromancer Games - Well put together modules, a little work to incorporate them into my FR campaigns. I've even just finished incorporating some of the deities Freya, Orcus, Tsathogga, and Set (which may remain as a primarily Mulhorandi deity) into FR. I also recreated Muir (and her portfolio) into a goddess by the name of Lysari into the realms. Thyr, Arden, Hel and Hecate are basically Tyr (without the edged weapon restriction), Lathander, Shar and Talona.
By far, this publisher puts out my favorite non-WotC products.
Whitewolf/Arthaus - Excellent job so far with the Ravenloft d20 line, I just wish they would build a few modules. I may even do a Feast Of Goblyns conversion in my spare time.
Green Ronin - Currently looking into these books, so far I like what I see. I'm seriously considering incorporating the city into the Realms somewhere, most likely as another port on the Sword Coast or on an Island Region just off the sword coast.
Malhavoc - Odd company for me, two of my favorite developers are here (Monte Cook and Bruce Cordell), yet I only consider Malhavoc for psionic gaming which unfortunately my group doesnt care for. I own the Psionic stuff from Malhavoc but am hesitant in using some of it.

Arcana Unearthed seems interesting but I cant see my group going that route anytime soon.
So far the only Malhavoc product I may use would be "The Banewarrens". I'll be moving Ptolus to the Realms as well when I have the time. Too many variant rules with their products to keep me interested, as well as references to these variant rules/classes in their modules making them a little more expensive as well as time consuming to prepare.
Just my $0.02