USB soundcards are now the most convenient and affordable way for plug and play recording. Many companies (ex. M-Audio, Cakewalk, Presonus, Line-6, etc.) now produces their own line of USB soundcards with various features that can satisfy the recording needs from simple 1-track stereo recording to simulatenous multiple ins. Most of them are capable of low latency recording and has good audio resolution and sampling rate. I suggest to search the net for the most appropiate USB soundcard/interface that would fit your requirements.
Right now I'm using Cakewalk UA-1G. It has a guitar/mic in and a stereo RCA input. Very portable, inexpensive and easy to use.