I've started to plan a Wizard build that may be worthwhile to take up to Legendary, based on this discussion. Comments and criticisms appreciated, as this is the first time I'm really planning a build this far.
The Tenacious Tinker Gnome
"Tinker Gnome" - requires Gnome INT +2. WIS -2, +6 lore
Final attributes at level 40:
STR: 8 DEX: 10 CON: 18 INT: 35 WIS: 6 CHA: 8
Alignment: Lawful Neutral (Monk)
Level Progression: 38 Wizard, 1 Rogue, 1 Monk
Feats (14 Regular, 10 Bonus):
Epic Spell Focus: Evocation (3) Epic Spell Focus: Necromancy (3) Epic Spell Focus: Illusion (2) Greater Spell Focus: Transmutation (2) Improved Combat Casting (2) Epic Spell Penetration (3) Maximize Spell, Silent Spell, Empower Spell Great Intelligence I, II, III, IV, V Epic Spell : Epic Warding
Skills: Concentration, Spellcraft, Tumble, Use Magic Device, Discipline, Lore, Hide, Move Silently (all 40 or up)
This is the default build that I've been suggested to make for a Wizard on HG, at least as far as feat progression is concerned. While not everyone suggests the focus in Illusion, gnomes get it for free at first level and the custom Epic spell for that school seems pretty nifty.
One may go pure Wizard, yet if one only spends points in Concentration and Spellcraft, one has about 260 unused skill points by level 38.