I heartily endorse any of the 1/48 Tamiya Jugs. Built the Razorback and Bubbletop myself and will probably be starting another soon. In my opinion, it may be the single best 1/48 mold out there, brilliant combination of detail, fit, and thoughtful engineering.
Other kits I'd recommend (really depends on subject, on what you're willing to spend, etc, but here goes):
A6M Zero - the newer Tamiya A6M3 and A6M5
Lavochkin La-5 - Zvezda (amazing kit, and cheap)
P-51 - Tamiya. Cockpit is kind of lacking, but the fit is extraordinary
PV-1 Ventura - Revell
F4U Corsair - Tamiya for the -1 variants (-1 Birdcage, -1A, -1D). Honestly the new Hobby Boss -4 looks decent enough, too.
F4F Wildcat - Tamiya's F4F-4 is a marvel. For the earlier -3 or General Motors-produced FM-1 and FM-2, Hobby Boss. These are solid, but canopy size and fit issues can be frustrating.
F6F Hellcat - Eduard. Unless you want wing-fold, then the Hobby Boss is a good choice, if you can live with the over-size canopy (me, I don't care as long as it fits).
Most Japanese fighters - Hasegawa. I've built their N1K1 George and it was phenomenal.
Bf 109 - Ugh. Too many choices. Eduard's new 1/48 Emils look really nice. So do Airfix's. The Zvezda F-2 is a gem, and cheap, but has more parts than a Dragon tank. Tamiya makes some older but well-engineered Emils, and Hasegawa's your go-to for late-model variants.
Fw 190 - See Bf 109. Eduard's 190 kits are nice, but have a reputation for fussiness. Hasegawa and Tamiya also offer various 190s. The Tamiyas aren't as detailed, but man do they build up quickly and easily.
SBD Dauntless - old Accurate Miniatures kit.
Avenger - old Accurate Miniatures kit.
TBD Devastator - the recent Great Wall Hobby release is really, truly something to behold.
P-61 Black Widow - if you're willing to drop the coin (and the extra coin for some aftermarket corrections) the GWH P-61 series is similarly impressive.
Spitfire - Tamiya for the Mk. I and Mk. V. Airfix for the Mk. XII. The ICM Mk.IX is supposed to be the best of that mark, but it's a PITA from what I've heard. Personally, I figure someone else will get around to it soon enough.