After some time the standard jQueryUI themes can get stale, boring, monotonous, and you need a fresh look. I've rounded up a couple very customized, non-"run of the mill" themes you should take a look at.
Absolution (Github) is a very clean theme with support for Uniform and Wijmo. Uniform, as its name indicates, styles form elements to have a uniform look, across all browsers. Drastically, improving the consistency of appearance. Wijmo is a snazzy widget collection providing both an "Open" (open source) and "Complete" (commercial) set of widgets. The developer has a few example widgets on their site showing off the look on all widgets. Another bonus is that development is handled with LESS, making it super easy to tweak. I will definitely keep this close by for future development!
A second theme worth a look is Aristo (Github), a port of Cappuccino. It has a bit more of an OSX look, but still a very clean, beautiful theme. An example of all widgets are included on the developer's site.
Just looking over the Absolution I am impressed with how LESS makes this look so more portable and themable than if only the CSS were provided. I definitely need to get up to speed on using LESS and the compiler. Better keep an eye out for integration on an upcoming project ;)
Both of these themes appear to work very well with Timepicker as well as the SliderAccess plugin, and are a nice compliment to most any jQueryUI based project! I'm still on the hunt for more quality custom jQueryUI themes for projects, so if you know of any please post them!