You need to get this one quickly as the next version is chargeable.

REAPER is a powerful but sensible Windows application designed for the recording, arrangement, editing, mixing and rendering of audio. REAPER provides a flexible but easy to use interface that is equally suited to amateurs and professionals alike.

REAPER is a small and lightweight application (the installer is less than 1 megabyte, which includes many effects and a sample project). REAPER is designed with both processing and user interaction speed in mind.

http://www.cockos.com/reaper/index.php

Basic features:

Support for an unlimited number of audio tracks
Audio tracks are all fully routable (multiple inputs, outputs)
Volume, pan controls and envelopes per track
Supports audio processing plug-ins (DirectX, DXi, VST, VSTi, and Jesusonic) with automation, easy chain manipulation and editing
Pitch shifting and time stretching
Fast, reasonable and usable Windows-style UI, working well on both low and high resolutions or multiple monitors
ASIO, Kernel Streaming, WaveOut, and DirectSound support for playback and recording
Reads WAV, OGG, MP3 and MIDI files, records WAV and MIDI files
Can render to WAV, OGG, MP3 if lame is installed
Full SMP support (can utilize 2 or more processors)
Multi-layer undo/redo support
Basic MIDI editing support
User creatable color themes

Advanced features:

Unlimited send/receives per track, with configurable parameters (pre-fx, post-fx, volume/pan adjustment/envelopes, mix to mono, phase, etc)
Any track can act as a bus, giving amazingly huge routing flexibility
Tracks can have one or more (mono or stereo) hardware sends, for analog mixing capability
Fully routable/FX-able folder tracks that can contain and group tracks
Item grouping
Ripple editing
Grid/snap support with highly configurable options
Markers
Unlimited takes per media item
Auto punch-in/punch-out functionality
Automatic record monitoring modes
Selection length granularity options as well as grid snapping
Tempo envelope (for grid lines/snapping/ruler), playspeed envelope
Project consolidation/export options (for rendering all or parts of any number of tracks to WAV/etc)
A UI and architecture that allows you to easily cut loops of many tracks simultaneously, without having to write them to disk
Support for plug-in generated media (such as click tracks, etc)
Project tempo envelopes for variable tempos in track, grid/snapping that supports variable tempos
64-bit floating point sample pipeline for high quality
Advanced recording and monitoring options -- examples:
You can route multiple tracks (inputs and/or media items) into a bus, and record THAT mixed down version.
You can record the input signal, or record the post-FX, post-track-rendere signal.
You can switch recording sources on the fly, even while recording.
You can arm/disarm tracks' inputs while playing or recording.

A sampling of qualities that makes REAPER sensible:

Sane, human readable, human editable, backwards and forwards compatible project file format
Options to build peaks for recorded files on the fly
Lots of control for the user to specify where recorded files go, etc, when dealing with many projects.
Template support to make it easy to load a project template and save it as a new project when you begin.
Input/output channel name aliasing (why view your inputs as "MOTU 896: Analog 1" when you could have them be "Vocal Mic", etc).
Options for automatically backing up project files to alternate paths, timestamped versions, etc.