People often talk about the power of spells like Sleep, etc.
Do people still talk about the power of Sleep? I'm astonished! in 3.0 and then 3.5 it was literally nerfed into uselessness!
Admittedly back in 1e it was a fantastic spell (take out 4d4 HD of creatures, none of which more than 4HD with no save? it was an encounter winner, and justified having that 1st level wizard along!)
But what is it now? 1 full round casting time to knock out up to 4HD total, and they get a save? I don't think I've seen a wizard take it, much less cast it, for years!
I do think there are still some problematic spells though:
Web: Save or not, you're still screwed by it. A successful initial save should allow you to just leave the area. I can't believe any designer has really read the web rules for years!
Wall of Iron: As I understand it the main argument about this one is economic. I think a 1hr per level duration would probably be fine (and use permanency for longer duration)
Polymorph: I like Eldritch_Lords solution better than anything else I remember seeing. Simple, straightforward.
Mirror Image: Personally I'd fix it by removing the scaling number of images. Just get 1d4 images. It is still a greeaaaat spell for wizards, but not quite so insane.
(I don't have a problem with comprehend languages, knock and so forth - I guess it is more of a problem if they appear in wands or cheap scrolls; without that they are taking up valuable spell slots and can't be used as often. Plus rogues are sometimes rather pleased to not have to always be the trap point man! If I was concerned about it, I'd just make it range: touch. That means that if a wizard wants to open a door/chest/something he is going to be just as vulnerable to the poisoned needles etc!
Holy Word/Blasphemy etc: Should be will negates for all effects, otherwise it is just insane (especially when used as a spell like ability by monsters...)
Most really problematic spells are introduced in supplements, to my mind. I've never allowed them, but as an example I'd look closely at any spell which claims to be a conjuration and thus avoids spell resistance but does 1d6 per level - it badly breaks the implied structure behind such spells in the PHB.
Problematic feats
Persistant Spell feat - should probably never exist
Divine Metamagic feats - also highly problematic
Problematic magic items
Incense of Meditation - they must have been insane to keep this one in!
Prayer Beads - the one that increases caster level is huge (e.g. with holy word, with damage causing spells)
Cheers!