A mixer would be useful if you plan to record several sources into a limited amount of inputs. Some good mixers such as Mackie have really good mic preamps suitable for recording. If you want (and really need) references for good mic pres, check out
Grace Design Model 101, Groove Tubes Brick and FMR Audio's
RNP 8380. Of course, you will need good mics (if you haven't already) and the condensers by Audio Technika seem to be getting good marks lately. You can't go wrong with the SM58 as a vocal mic, too.
Instead of the
audio buddy and separate audiophile, consider the
Presonus Firebox. The Firebox runs on firewire so you don't have to open up your pc (so long as it has firewire ports) and the firebox even has 2 mic pre's so you can forego getting a mic pre until you absolutely need it. You can also try M-Audio's firewire equivalent, the
FW 410 but I've heard the pres on the Firebox are better.