All Pokemon have an IV (Individual Value) for each of their six stats (HP to Speed), which increases that stat slightly. Unlike EVs, which must be earned, IVs are determined upon capture--or in the case of Pokemon eggs, after hatching.
To determine your Pokemon's IVs, you can use an online IV calculator. For breeding though, there's a quick way to check your Pokemon's perfect IVs (with a value of 31) and that's to consult the IV judge inside Kiloude City's Pokemon Centre.
If you show the judge a Pokemon, he'll tell you its best stat(s) and remark about their characteristics. In our breeding section, we tell you how to acquire Pokemon with many perfect IVs. So if you follow our tips, you should have Pokemon with some perfect IVs.
In which case, he should mention a list of stats and then say "Stats like those... they simply can't be beat!" This means all the stats he mentions have an IV of 31 , the best you can get. If he mentions every stat and then that phrase, that means you have a Pokemon will all perfect IVs!
Once you've nailed the IVs, it's good practice to write them down somewhere, especially if you intend to use that Pokemon for training or breeding. Luckily, as it happens, there are 6 stats and 6 markings you can apply to your Pokemon via the PC.
What you can do is, for each perfect stat, use the 1st marking for HP, 2nd marking for Attack and so forth. So a Pokemon with the first five markings has perfect stats except in Speed.