I've always liked dwarves. There've been a great many d20 racial splatbooks, few of which I've liked, and the only one I own is for dwarves. Now, WotC has decided to do its own racial splatbooks, and the first effort, detailing dwarves, gnomes, and a brand-new race, the goliaths, is actually a very good product.
One of the striking differences between Races of Stone and, say, the Planar Handbook, is that the primary focus of this product is what's known as "fluff"; i.e., information that is not strictly related to rules, but that details things like history, mannerisms, behavior, etc. For example, dwarves make a great variety of their clothes from root fibers! This has no real game effect, but it's nice information to have. There are sections for each race in this book, with the goliath section being a tad longer, since they're new to Races of Stone.
Speaking of goliaths, they're a primitive nomadic mountain-dwelling race; they're almost like evolved apes. They're very competitive, and quite strong. Their society is detailed in a lot of detail, and there are rules aspects that are non-obvious; despite having a Dex penalty, for example, they have a great fondness for ranged weapons.
Also included are variant races...chaos and whisper gnomes, dream dwarves, stonechildren, and feral garguns (who're relatives of the goliaths that live in even more unpleasant circumstances).
However, there is a very nice proportion of game mechanics goodness to be found (this is known colloquially as "crunch"). There are many new feats that are appropriate for the given races, new equipment (like exotic armors!), racial substitution levels (where you get an alternate class ability in place of a standard one, but only if you qualify by your race or other factors), and quite a few nifty prestige classes. There are a few spells and magic items (like forges that let non-casters create magic items, with some severe limitations), too. There are even adventure seeds that are more appropriate for the races of stone, as well.
Quite possibly the best new thing is that they don't assume you just have the Player's Handbook, as there is support for the Expanded Psionics Handbook, in the form of additional psionic feats and powers! This is very new, and very welcome, to boot.
I'm quite pleased with Races of Stone. It certainly washes out the bad taste of certain previous releases. I wholeheartedly recommend it.