Melodie's Tone Pops Grill is a commercial VST that runs $0.99, so it's not really worth it if you're looking for total customization, but it's got some very nice real pads that can be used for everything from a dark synth to a siren that's been "spiced" up. It's a very slick synth, and you can hear an example of its sound playing here:
It just occurred to me that I may be from the "don't make more work for yourself" school when it comes to my hardware. I play acoustic drums and piano, electronic drums go over my head, but that isn't stopping me from looking at VSTs that I can grab and play with in Cakewalk. If I start writing down all the VSTs I play in a session, I'll start from scratch. I don't want to spin my wheels.
While he's known as Mixcracker, there's a guy who goes by the name ApeKit on IRC, and he's also doing VSTs, including some great synth plugins. If you're really looking for a VST, check out his DX25 and Kickersaurus plugins, which go for about $23 total. d2c66b5586