Software that can make a mountable image of my hard drive

Disk2vhd allows you to capture volumes to .vhd files:

Disk2vhd is a utility that creates VHD (Virtual Hard Disk - Microsoft's Virtual Machine disk format) versions of physical disks for use in Microsoft Virtual PC or Microsoft Hyper-V virtual machines (VMs).

The difference between Disk2vhd and other physical-to-virtual tools is that you can run Disk2vhd on a system that’s online. Disk2vhd uses Windows' Volume Snapshot capability, introduced in Windows XP, to create consistent point-in-time snapshots of the volumes you want to include in a conversion. You can even have Disk2vhd create the VHDs on local volumes, even ones being converted (though performance is better when the VHD is on a disk different than ones being converted).

The Disk2vhd user interface lists the volumes present on the system:

It will create one VHD for each disk on which selected volumes reside. It preserves the partitioning information of the disk, but only copies the data contents for volumes on the disk that are selected. This enables you to capture just system volumes and exclude data volumes, for example.

You can attach these VHDs to the Disk Manager, you can in fact even boot from them in some condition.

As you didn't mention the OS, I would suggest the tool dd. But be aware that you have to be careful about the parameters. You just type

dd if=/dev/<source partition> of=/media/<your_usbdisk>/foo1.img bs=64k

and get a dump of the said file system in the said file.

I haven't used it, but I think Disk2VHD might be what you need.