This comparison is a bit insane but anyway and to keep it short the iPad is a tablet that can be used as an e-reader and the Kindle is a dedicated e-reader that cant be use as anything else(plays mp3 though).
The Long Version:
The most important thing about Kindle is e-ink, paper like screen that is very confortable for the eyes. If Im not mistaken it uses a 16 gray level palette. Battery life for a Kindle is pretty good, aproximately over a week. Finally the worldwide 3G connectivity of the Kindle is a big plus even more when u don't even have to pay for it.
The iPad, well this is not a dedicated e-reader like I said, it doesn't offer e-ink but an ISP LCD with a resolution of 1024x768, full color screen obviously. Battery life of 10 hours which is nothing compared to a Kindle but with an iPad ure not just limited to read books. The iPad features a 3G model, however it comes with a dataplan of about $30 a month, but again, while on the Kindle u can only download books on the iPad you can browse the entire web, download movies, tv shows, stream video, go on YouTube, facebook, ur email and all those things ud do on ur regular PC.
The Kindle is big joke compared to an iPad. Its only appealing to those who love e-ink cause seriously theres nothing else there. I wouldnt carry around a device that can barely manage to produce 16 shades of gray, takes a life to load the next page and it renders black without an external light source.
Apple set the bar high with the iPad. Currently they own a market that was abandoned over a decade ago, mainly because these first tablets didnt have a good multi-touch OS available back then. Just recently Samsung managed to release Galaxy Tab, which is IMO a big failure but its just the first one of many others to come. There will be raining tablets next year running Android. The market is ready for tablets, but what the market is definitely not ready yet for is over priced e-ink.