Man, foweyman's pics rock.
Lake Reflection is gorgeous (in fact it's my profile photo) but kind of ways off the JMT.
Sixty Lakes Basin on the other hand is more or less right there and, IMHO, probably the prettiest spot in the whole Sierra. Big statement I know. Lots of smaller lakes as the names suggests but that gives it kind of a japanese garden feel. All these smaller, intimate little scenes. Just awesome. The frogs are an added benefit since they're so uncommon in the range.
I'd also consider a trip up Banner and possibly Ritter if you're solid on class 3. It's pretty exposed for the grade.
Always wanted to hit Center Basin but haven't made it yet. Since you're planning on making a side trip to Tyndall though, you could take Center Basin to Junction Pass, which drops you down around Anvil Camp on Shepherd's Pass, which will take you right to Tyndall. If you're in the neighborhood, might as well tag Junction Peak as well.