For your legs, most riders find it most comfortable not to wear tights or leg warmers in the rain (they just suck in the water). If you're afraid of getting cold, just coat your legs in vaseline. You can buy expensive, sport-specific gels for your legs, but I find vaseline works pretty darn well.
Rain typically means dark skies, so don't forget your yellow or orange lenses. These are actually better than clear lenses because they'll help with depth perception. Again, it's a preference issue whether to wear glasses in the rain, but for most rides, where you'll be in close proximity to other riders or cars, the added eye protection is worth the annoyance of raindrops on your lenses.
If only cycling glasses had little windshield wipers. Yes, your glasses will get wet! Bummer. Some riders like to wear a visor under their helmets if it's raining to help keep the rain off their glasses. You can use a baseball cap or a cycling cap, but remember that this will affect your helmet fit (you'll likely need to loosen the straps).
Long finger gloves are great in the rain, however, most are not waterproof. If you're afraid of your fingers getting cold (making shifting and braking a challenge), put a pair of surgical gloves on under your cycling gloves. Yes, your hands may get sweaty inside the surgical gloves, but your fingers will stay warm. Worked great for me in Alaska!
For cold feet, you can do the same type of thing. I layer a plastic shower cap under my socks and then wear a pair of booties. Yes, the booties will retain water (making your legs heavier), but the shower caps will keep your feet warm.
When the skies are dreary, most drivers won,t expect to see cyclists on the road. So make sure to be as visible as possible. Wear bright colors (yellow, orange, red, or pink are really good ^ blue, green, gray or black aren,t visible). You can add reflective stickers to your helmet, wear a reflective vest or bands, and add a red blinkie light to help ensure you,re seen.
BTW, don't forget to eat & drink even though you may not feel the need in the cold, wet weather. We get just as dehydrated in the cold as we do in the heat, but most folks don't feel the need to drink when it's colder out.
And lastly, remember that you should ride more conservatively in wet conditions. Wet roads can be slippery, so allow yourself more time to brake (don't forget, your rims will be wet, too), and slow your speed through the corners. Your tires will have less rolling resistance on wet roads, so play it safe and take your time.
With a little planning, riding in the rain can be fun! Just imagine yourself as a 10 year old splashing in the puddles!
