What D&D books should I look at?

Are there any D&D books I should look at to compliment my Conan game?

I ran across a book that looks pretty neat called HEROES OF BATTLE. Since I'm considering running some large battles in my game (probably using the narrative system in Free Companies), I'm wondering if that book would prove useful.

Another I thought looked neat, but wonder if its necessary, is a book called the RULES COMPENDIUM.

Any other D&D books that you think would be helpful for a Conan campaign?
Since your campaign takes place in the north you may want to take a look at the different D&D books that cover environments.

Frostburn - special rules for a Northern-sub arctic to arctic type environments.
Stromwrack - special rules for water based campaigns
Sandstorm - special rules for a Desert Based campaign.
Cityscape - special rules for campaigns based in major cities.

There are some great rules in these books as well as a small section on creatures unique to these environments. Some of these creatures are easily portable to a Conan game some aren't.

Obviously some of the information in these books will be no good but over all they are an awesome read.
I personally use this and that from the Scarred Lands books (by Sword & Sorcery Games), as it a dark fantasy.

Wilderlands by Judges Guild is also worth looking into.
Does anybody have a good, in-expensive source for 3.0 and 3.5 D&D books? It seems like I should find some good deals now that 4.0 has been out a couple of years.

Got a link for a discount RPG house with D&D books?
my group has a ton of 3.5 edition D&D books since that was basically all we played prior to Conan. we just wanted to get every book out there and we nearly did. of course many books were 80% useless and just filled with stupid feats and even stupider prestige classes but that's another matter. my point is that the only book out of all them that is ever even looked at and used during our Conan sessions is the Rules Compendium. As Nialldubh said, it's good for a quick reference i'd say it should be the first pick if you're looking for useful 3.5 books. All the rest are collecting dust for me. I have every Conan RPG book, the Barbarian books, and the 3.5 D&D Rules Compendium in my "Nerd Bag" and so far, I don't think I need anything else. Except for the next Conan rpg book. Whenever that happens.