Last few projects of mine:

- Prototyping: no graphics (text only); drew myself (so bad that I reverted to text only); free libraries

- Publicly available: paid a friend of a friend; hired someone on a popular outsourcing site (after I paid them it turned out that they stole it from a not-free illustration library); free library; paid for not-free library

- very limited (<50 users) beta: all of the above plus not-free-library with watermarks (users actually liked this because it gave the site an authentic, work-in-progress, exclusive vibe--their words)

Honestly, graphics are overrated and people of all walks of life appreciate high-information density above all else. Landing pages for marketing campaigns convert slightly better with fancy graphics, so you ideally want both. Most companies only have the pretty pictures, which is both a shame and an opportunity.