Anything published after Monster Manual 3 uses all the new updated damage and can be run as is (or with whatever tweaking you like best). Every book that came out after is similarly good. So Monster Manual 3, Demonomicon, Dark Sun Creature Catalog and Monster Vault are the best resources for monsters. Additionally dungeon magazine monsters published after MM3 are generally following the new maths - except when they use older monsters. This isn't a big issue as they never publish anything in paragon/epic anyway, where the maths makes the biggest difference.
Anything published after Monster Manual 2 (maybe a little before) uses the correct HP and defenses for elites/solos. You just need to upgrade the damage here and most of these creatures are fine. Bearing in mind you shouldn't do this at all for some, like Chaos Shards (brutal level 4 artillery with static shock IIRC). Creatures from MM2 need their accuracy changed, brutes have +2 (in general) to attacks, soldiers -2 (in general) and artillery are usually alright (as they had higher attacks in the first place).
Anything pre-MM2 needs to have its defenses looked at (if it is an elite/solo), because this was changed by MM2. Accuracy also needs looked at. HP of solos need to be looked at as well. Basically you need to do a fair amount of work on most aspects of older solos. There are some exceptions, the Ancient White Dragon in the original MM is very close to the updated damage and accuracy. It's a really curious why this is actually.
As an important aside, heroic tier monsters from older books tend to be usable as is. They aren't as "clever" as newer creatures, but they will function 100% fine without needing modification. Paragon and Epic monsters before MM3 do not work very well.
Edit: Once I get the time, I will post a really comprehensive thread + examples of designing newer creatures. One example per type (Soldier, Brute, Controller etc) and some example solos (which honestly are the most intensive work wise to get functioning well).