I have almost no experience as such, but have been thinking about trying one out.
I did get a FiiO E6, which is just as basic amp with some eq settings. It provides a LOT more oomph than the standard out put of my iPod, but mostly that just takes the available volume range well beyond what I want. The other use I have for it (was only about £20) is getting enough output to plug the iPod into any line in, which it does just fine.
However, I have been looking at a desktop dac/amp… been thinking about trying a Aune T1. Or, might also consider something portable to use just as an amp with the iPod and as dac/amp at my desk.