I use the Whosamung.us widget which you just put in a text widget.

Some plain HTML can be put into text widgets, but allowable HTML is limited. You also can't use javascript or PHP for security reasons. Direct flash embeds are also not allowed although some of it can be used with the gigya shortcode. The gigya shortcode is not supported and the fact that it works here is sort of a fluke. If at some point abuse of it becomes an issue, it will vanish without even a puff of smoke.

Tell us what you want to do and let us see if there are some workarounds. Over the years users and we volunteers have come up with some ways to do things here that normally would not be possible.

The other choice would be to self-host an installation of the wordpress.ORG software on a third-party hosting service such as godaddy, bluehost, etc., and then you can hack, slash and burn your site to your heart's content. Self-hosting comes with additional responsibilities and in general will run you around $10 to $25 per month, all costs considered.