How small do you mean? Some of my favorite small orchids are
1) Den. lichenastrum/prenticei (I have four and the flowers are all a little different).
2) Schoenorchis scolopendria and Schoenorchis fragrans. I love the little fragrant purple flowers.
3) Angraecum didieri, distichum, and leonis. I am still trying to get over the Angraecum obsession I once had. I have the 'large' Angraecum magdalenae, too.
4) Bulbo frostii has neat flowers and a cute plant form out of bloom.
5) Haraella rectrocalla blooms all the time and has fragrant flowers. It needs quite a bit of humidity to be happy so I keep it in a table-top terrarium.
6) Phal japonica
7) Leptotes bicolor is definitely a good choice. I am tempted to get a few more varieties of Leptotes.