PediSuite would be the best peds application for you in my mind and is well worth the cost (relatively minimal at $45. You can get a full function trial period for free).
MedCalc
Medical Eponyms
Mobile Merck Medicus (free and actually has a fair amount of peds content)
Epocrates (is OK, kinda lame UI on WinMo, but WinMo is kinda lame in general)
See if Pepid Elements is offered on WinMo (it's a freebie app for the iPhone/ iPod Touch) for a nice little toxicology program.
If you're an AAP member (when in residency or beyond) you can choose your RedBook format which includes electronic (it's nice on my iPod)
If you want to spend bigger bank you can look into LexiComp's peds offerings (there are a lot of institutional discounts out there so look for them) and Pepid (which is too rich for my blood, but generally well regarded)
Since pediatricsonhand.com is pretty much dead (although some of the reviews for the programs may be relevent since there hasn't been a ton of WinMo app development for peds of late),
http://www.pda4peds.com/ is a decent resource to look for some apps.
