Arguably the best PokéDex app you can get. As with the previous app, this one comes in a Free (Lite) version as well as one that you have to pay for. Unlike the previous however, I would strongly suggest buying the full version if you are a serious pokémon player ($3, which is WAY cheaper then the giant paperback PokéDex guides at retail stores). Not only does this Dex offer information on the pokémon, when they learn moves, thier egg groups, type matchups, etc.. but if you buy the full version if comes with an EV/IV tracker, an EV/IV Training Guide, and an EV Tracker. This Dex is also easy to use as you can search by Pokémon, Moves, Items, or Locations. You can even choose which game you need information for. The Dex includes seperate entries for Ruby, Sapphire, Emerald, Diamond, Pearl, Platinum, Heartgold, SoulSilver, Black and White!
Unfortunately, this Dex lacks information on when/how pokémon evolve. This really is the ONLY main problem this Dex has. The other is that there needs to be an update which lists the TM/HMs correctly for Black and White in the Item Seach (for example it lists TM 01 as Focus Punch, but that is based on D/P/Pt/HG/SS. In BW TM 01 is Hone Claws).
Potentially the best purely PokéDex based app when it comes to being visually appealing and easy to search. It's 2nd to Lukomon, however, since it's just a Dex and doesn't offer any information on items, nor does it have tools like the EV Tracker. It does do very good job of giving ample room to everything on the screen, sometimes the Lukomon Dex doesn't which causes me to somtimes press a wrong button or link. However, the main downfall of this Dex is the lack of a BW update. If your just playing Diamond, Pearl, Platinum, Heartgold, or Soulsilver only for fun however, get the free version of this Dex rather than Lukomon. You'll save money, and have pretty much everything you need outside of the tools.
After talking about several good options, it's time for the worst. Pokepedia is visually unappealing compared to other the other PokéDexes. Not only that, it suffers from horrible lag time, only goes through the Gen IV pokémon (Diamond, Pearl, and Platinum), and offers less information than other Dexes. The only thing this dex offers that others don't is some trivia about each pokémon... which is hardly worth the wait time it takes to scroll down to the pokémon you want to see. The creaters, Asobi Time, say the have other pokémon apps availible in the iTunes Store but if they are as bad as this one... I wouldn't waste my time.
Anyway, there you go. If you have any comments about these apps, or if you've found some that work great for you, let us know!