Find yourself a really well fitting wetsuit with a slick lining like the Henderson Gold Core or any of the numerous clones out there. I personally don't subscribe to the whole titanium retaining warmth, but I DO know that a suit which fits well (not baggy anywhere) together with having a slick lining (to form a seal against your skin) will all but eliminate water exchange and keep you warmer. I was the only student to shiver during our pool sessions, and was always the coldest after the dives, but once I got a suit meeting the criteria above (I settled on an aquaflite 7mm) I was able to dive at depth (around 60 fsw) and stay down about 30 minutes before I started getting cold. The water was 38 degrees! I can't stress enough how much of a difference the new suit made. I'm not ready for a drysuit right now, and I know that I'm likely to get cold on especially deep dives, but for the dives I usually do, (less than 60 fsw and usually warmer than 45 deg F) a nice 7mil does the job for me. My old suit was an older 7mil Farmer John, but it didn't fit quite as well, and the fuzzy lining let in way too much water. The new suit also has an attached 7mil hood.