Note: Specifications and options change often so use this post as a starting point.
Some Things to Consider
Are you a 501(c) or fiscally-sponsored? If you are fiscally-sponsored, your choices will be limited because many platforms require a 501c3 number to set up the "event." If your fiscal sponsor will let you use their 501c3, then you will have more options. Fiscal sponsors that work with multiple organizations are less likely to let you do this.
Do you need to set up teams? Some events are designed so that people can join a team. Some platforms offer this option - others don't.
Think about how tech savvy your fundraisers are. This is subjective, but if your fundraisers aren't used to using technology then consider a simpler platform.
How much are you willing to pay? Fees vary across platforms but in general, the more you pay, the more functionality you get.
Some Platforms to Consider

Razoo is one of my favorite platforms because their fees are so low (4.9% all inclusive with no monthly or setup fees) and their customer service is fantastic. They offer teams functionality.
Things to consider: Their system is tied to 501c3 numbers, so if you're fiscally sponsored, they may not work for you. I found it difficult to navigate between the organization's landing page, team pages, fundraiser pages, and event pages. The fundraising pages are not as slick and clean looking as other platforms, though their home page was recently updated so I wonder if design updates are in the works for the rest of their site.
www.razoo.com

The thing I like about Crowdrise is that they are fun. Their communications are peppered with humor and crazy challenges. Customer service is great if you choose a plan that includes Premium Support. Plan pricing ranges from 7.9% + .30 per transaction (no monthly fees) to 5.9% + $199/month (with annual commitment). The latter plan is worth it if you anticipate hundreds of donations.
Things to consider: This system is also tied to 501c3 numbers like Razoo. Their team functionality and individual fundraising pages look great and are clearly tied to the fundraising event, which is also clearly tied to an organization.
www.crowdrise.com

Launcht are the new kids on the block and I think they have a lot of potential. The platform is highly customizeable and designed so you can use Launcht as a website for your fundraiser (you can additional pages, for example). Some examples of customization include adding a start and end date for your campaign, making it private or public, and listing questions for participants to answer to complete their profiles. Pricing is high for small organizations that are unsure of their ability to raise money -- $495 setup fee, $295/month, and 1% of donations. It's worth checking in to see if there's any flexibility there.
Things to consider: Launcht does work with fiscally sponsored organizations, which is a big plus. The landing page looks great but is missing the option of adding a thermometer to see overall progress toward goal. Once you launch your site, there are certain things that cannot be changed. Launcht has a lot of promise but they're are still working out some kinks in the system.
www.launcht.com
Notes on a Few Other Platforms
FirstGiving: One of the more popular peer to peer platforms that nonprofits are using. They must be doing something right! They have a set up fee and I haven't worked with anyone willing to sign up without test-driving it first.
Rally: Nice simple, clean pages. Low fees - 5.75%.
CauseVox: Nice design, build out a whole event site on this platform. They offer a free trial.
Remember, there are other platforms out there -- this is just a sampling. Kickstarter and Indiegogo are used for Crowdfunding a specific project, which is different than this kind of fundraising (also called peer to peer - see last blog post). Please leave a comment if you know of any others or if you want to share your experience using any of the above. The specifics of fees and functionality change regularly, so please remember that everything here is a starting point for your own research in finding the best platform for your organization. Or you can contact us and see if Aril Consulting can help you crowdfund successfully!