The main problem with tube preamps in this price range (used) tends to be noise - not in the sense of prominent spitting and motorboating like cheap tube equipment, but they obscure detail compared to better tube pre's or solid-state designs. You also don't tend to get much of a power supply. Unfortunately, things start to get a lot more interesting around $2k.
I would second the above recommendation of a used BAT (they're differential balanced and relatively quiet).
Another well-made preamp that can be had for a bit more than $1k is the Sonic Frontiers Line 2. It's unspectacular, but does less harm than most things in this price range (it's also fully differential balanced and quiet). It has a good remote and an outboard power supply, which is unusual in this price range.
One of my dealers thought so little of the Audio Research LS-2B it that he insisted that I order the $800 cheaper LS-3 (which I did).
The Audible Illusions are solid high-end preamps and have outboard power supplies, but customer support is notoriously poor. The circuit does not have a soft-start function or tube rectification, and because most people running it turn the preamp on and off, it blows tubes a lot as a result - it's an excellent example of the need to keep most small-signal tube gear powered up 24/7 in order to extend tube life. It has hot-rod dual volume controls (a separate volume control for each channel), which some people find annoying (notwithstanding the improved performance), and no remote. It has a very good built-in phono stage.
The CAT is a true high-end preamp, but even the Mk. I's usually go for $2k. They also have too much gain for a lot of amps (there's too little range in the volume control), and don't have a remote. The power supply is hardwired to the main console with a super-thick, inflexible umbilical that could tether the Queen Mary to a dock - it's user-surly in this respect. It has a very high-quality on-board tube phono stage.
I would steer clear of entry-level conrad-johnson gear.
The vast majority of tube preamps have difficulty driving long interconnects - try to keep the interconnect running between the preamp and power amp to two meters or less. And whatever you buy, retube it before running it (the beauty of tube equipment is that when you retube it, you basically have a new piece if gear). Preamps have a subtle effect on the sound of a system and can take a long time - months - to properly evaluate, so be patient. "Subtle", however, does not mean unimportant - quite to the contrary, as every good system has a good preamp. Good luck.
Oh, interconnects - Kimber Hero works very well in a lot of systems, but it's unshielded, so it can be noisy in the wrong system.
