Zendesk is definitely the choice for a ticketing system...we use it internally for bugs. If you're looking to collect feedback and get a sense of what people want to see in your product, UserVoice is the simplest solution for your end-users. You integrate the feedback form wherever is best for you and your customers can easily submit and vote on ideas (even using the login credentials from your own site, if you'd like).
If anyone has any questions about UserVoice feel free to drop me a line. Also, we do have a 50% discount for startups for the first 12 months. Just enter the code onstartups101 when signing up to get that discount.
evan at uservoice dot com