Introduction
About the most fun modifiers to load up in are ones that add to your chance to find Magical Items. The main goals of the game for most are to level up, and to find nice items. Better equipment is fun to find, and makes your character more powerful, and adding Magic Find, or "+MF", as it's called, is a great way to get better stuff to drop from monsters and chests.
You can get +MF on most every type of item in the game. Gloves or Boots or jewelry with +10% or 15% or 30% won't make a real noticeable difference on their own, but as you accumulate more and more items with these bonuses, you'll start to notice that you find more Rares, Uniques, Set Items, etc.
The easiest way to add it is by socketing perfect topazes into Armor or Helm. Getting a hold of 4 socket armor and a 3 socket helm shouldn't be too hard, and that's 168% right there.
There is no cap on magic find, but there are diminishing returns as of v1.09, see the table below for the actual stats. You'll start to notice improvements at around 100% Magic Find, and by 200-300% it will start to get very addictive.
Characters who can kill with their skills, especially Sorcs, are the best at going to a very high Magic Find, since they don't need equipment for their offense. Barbarians are very good also, since they get huge hit points and resistance bonuses form their skills and stats, so need less good equipment to survive, and can dual wield Gulls or Ali Babas for a huge MF bonus from the weapon slots.
It can be a lot of fun to load up all your best +MF stuff and do item runs on normal or Nightmare where you don't really need much good gear to survive. Killing the bosses, Mephisto, Diablo, and Baal are the best drops and they can can all be reached pretty quickly, especially Meph. You won't get the best stuff, Elite set or unique items on Nightmare (some of the lowest elite item types can drop from Baal or Diablo, but your odds aren't good) but there are lots of very good Exceptional items that can be found there.
For obvious reasons, Hardcore characters have to be more careful about going all out on +MF stuff. Usually resistances drop very low when switching to the magic find equipment, and one Lightning Enchanted boss that you would normally tear right through can be suddenly deadly if your Lightning Resistance is -22%, rather than your normal 65%. For example.
Magic Find Percentages
Magic Find doesn't boost your odds of finding everything equally. It's all the same up to 100%, but after that your odds of finding Rares, Sets, and Uniques drop steeply. Blizzard added this in since it's possible to get such huge Magic Find numbers in the Expansion, and they didn't want it to be so easy to find the really good/scarce stuff.
You can see exactly how much in the table below.
| Magic Find | Magical * | Rares * | Set Items * | Uniques * |
|---|---|---|---|---|
| 0% | 0% | 0% | 0% | 0% |
| 100% | 100% | 100% | 100% | 100% |
| 150% | 150% | 146% | 145% | 141% |
| 200% | 200% | 185% | 183% | 171% |
| 250% | 250% | 220% | 215% | 193% |
| 300% | 300% | 250% | 242% | 211% |
| 400% | 400% | 300% | 287% | 236% |
| 500% | 500% | 340% | 322% | 253% |
| 750% | 750% | 412% | 382% | 280% |
| 1000% | 1000% | 460% | 421% | 295% |
| 1200% | 1200% | 494% | 448% | 305% |
| 1500% | 1500% | 520% | 468% | 312% |