One good, simple, inexpensive alternative is the MicPort by a company named Centrance.
It's basically a USB interface that acts like a USB mic, except you can use any mic. You plug the mic into it and it into the USB port. It's simple in that it doesn't require any drivers and is compatible with almost any software.

It acts as a preamp and (unlike USB mics) as a very high-quality playback device, so you can overdub with no latency. 24/96 recording, I believe. It also has phantom power and the whole shebang is powered from the USB. I've used high end condenser with it and it works fine.

It's very portable -- a little cylinder about half the size of a cigar.

It only costs about $150.

The downside, of course, is, like a USB mic, you can only record one track at a time. But the company offers free software that allows you to use more than one at a time.