I generally don't like ability y having a lot of per-requesits to get (aside from level). Just like those feat-trees from 3e, talent trees also often mean getting things you Don't want to get something you Do.
However, if you like Talent Trees, take a look at Exalted.
In Exalted, you have various character abilities (equivalent of skills): Archery, Medicine, Martial Arts, Dodge, Occult, Athletics, Thrown, Craft, Melee (weapons), Presence, Performance, Larceny, Investigations, Survival, Bureaucracy, Socialize, Sail, Stealth, Resistance, Ride, Lore, Linguistics, Brawl (1st ed only), Endurance (1E only), Integrity (2e only; resisting social attacks/body transmutation attacks), and War (2nd only; commanding large scale battle).
Each skill has several trees of Charms (4e equivalent of powers) associated with it. For instance, Melee has a tree for multi-attacks, doing more damage with single attacks, and parry-related powers.
Taking a page from Exalted, it would be interesting if they tied Talent Trees to skills. It's unlikely to work for some things in D&D - combat related abilities aren't skills. But things like stealth/search/etc are, and feats/whatever that affect those could be tucked under a tree.