I transferred mine to Lake Michigan Credit Union HSA. Recently (this year?), they started allowing HSA investments. You must keep $1000 in the regular HSA (which still has a small interest %, better than nothing), but anything more than that $1k can be put in investments, including many Vanguard Admiral options.
Right now mine are allocated 25% each in:
Vanguard 500 Index Admiral
Vanguard Developed Mkts Idx Ad
Vanguard Mid Cap Index Admiral
Vanguard Small Cap Index Adm
No fees. They send a debit card for access to funds. However, with investment options like this, I plan (health pending...) to pay out of pocket and let these funds grow. Tax free in, tax free growth, tax free withdrawl. With investment options like this and no fees, it seems like an outstanding deal to me. Wish my employer would offer the HSA again (they funded half of the amount I now have).