If your clip is very short you could try a strategy someone on Ken Stone's site uses - compress to photojpeg at as high a quality as you can while staying within the 100MB limit. Since photo jpeg doesn't compress temporally, you only end up going one pass through a temporal codec (whatever flavor of flash you tube is using). But this only works for a VERY short clip.
Cutting your frame rate down to 15 should help too. I notice there's now an option to upload pretty gigantic files to You Tube using a program they offer for download, but it only runs on windows. WIth that option you could theoretically do photo jpeg or dv for longer clips. My best results so far on longer clips have been with h.264 even though You Tube claims they don't support it. Occasionally they'll reject an h.264 - it looks like these are usually close to but still under the 100MB limit, but I don't have enough data to know for sure that's the trigger. But it ends up in a low quality flash encode no matter what, so anything with detail and motion is just going to look like crap on YT. On the iphone, though, SOME of it looks pretty good - probaby because those particular clips are h.264 from a relatively high quality original upload. Brook _______________________________________________________ Brook Hinton film/video/audio art www.brookhinton.com studio vlog/blog: www.brookhinton.com/temporalab