If you want to go out of Onion Valley and stick to the main trails your only real option is to do an out and back over Kearsarge Pass. Otherwise your options are some hard cross country routes over Shepherd Pass or University Pass . The only thing that I know about Taboose Pass is that it is steep.
A good circular route is the North Lake to North Lake route out of Bishop. You can do a 85/15 main trail/cross country route that has a fair amount of ups and downs. Some of the most beautiful scenery in the entire Sierra can be found along this hike. You start at 9300', go up to 11,200' at Piute Pass and then down,down,down to Hutchison Meadow at about 7500' where you join up with the John Muir Trail. From here you turn south and hike to the Darwin region, this is where you deviate from the JMT and go "cross-country". This is in actuality, not cross country, there is a fine trail that will take you through Darwin Bench, up to Darwin Canyon and over Lamarck Col.From the Col you head down about 5 miles to North Lake where you started. This is a good 4-5 day hike.
Here is a website that has the above route in an abbreviated version; it's starting in the opposite direction, going over Lamarck Col first. The mid 2/3 of this route over Alpine Col and around Goethe lake is all cross country and is very difficult.(The link shows the route bypassing the descent into Hutchison Meadow, the link up with the JMT and bypassing the Darwin area, which, I think is the nicest part of the trip). If you are not comfortable with 35 degree talus slopes stay away. The pictures though, show the wonderful scenery along the route.
http://171.64.169.61/.mh/darwin_0902/index_web.html