please review our online load testing service - loadimpact.com
luminousbit: I love the site, HATE the pricing.  I'd really like to pay for the service, but what I REALLY need is:1) Run several low user tests (200-300) to tweak server settings, app code, etc.  
2) Then run one or two big tests (1000+) just once to see the results.I MIGHT need this at most once a month.  That just isn't worth $200 per month.  I'd much prefer a subscription for the lower levels of consistent use, and then be able to purchase an additional once-off very large test for maybe $10-20 each.