One of the really useful tools you can have as a Ham is an antenna analyser, which enables you to understand better how your antennas and overall RF installation are behaving/performing at various frequencies.
Sark-110 to KX3 Size comparison
At the very least, an antenna analyser will let you check the standing wave ratio which, in a very simplified view, is the amount of energy that is being reflected back into your transmitter and not being sent out. A high SWR usually is not a very good thing, though a low SWR does not always mean you have a perfect antenna either, that would be too easy – a 50 Ohm resistor connected to your amplifier will always give you a 1:1 SWR but won’t help you much if you want to make contacts!
Still, understanding how your antenna behaves depending on the frequency, see exactly where it resonates, and how its impedance evolves, is extremely useful. There are many types of antenna analysers on the market, from really cheap kits, to totally awesome tools like the Agilent Fieldfox, or even more advanced stuff that costs as much as a small house… I found a good article at rigexperts which explains a lot of different possible architectures, a good read.
With this in mind, I recently purchased a Sark 110 from Seeed Studio, who sells it for $360 as of January 2014: this antenna analyser is designed for HF to low VHF bands, with a 0 to 230MHz range. This makes it perfect for hams, though being able to include the 70cm band would have been a nice touch. The Sark 110 is fairly priced, especially for what it does: you get much more than a VSWR indicator here!