I used the search function, but it didn't seem to work out well for me. So I wanted to ask what are the general differences between a roller and a trainer; their pros and cons?

I have both. I first picked up a trainer, Cycleops fluid model. I used it for a winter. I was happy with the way it simulated resistance. Out of curiosity I got a set of rollers with a mag resistance unit . If I train indoors, I primarily ride rollers. I think it keeps the workout more interesting, plus rollers build balance and pedal stroke. The only thing I can't do on my rollers is hard out of saddle sprints. I just jump of the drums. I'm going to remedy this with building a DIY emotion setup.

Rollers in the morning, Trainer in the evening

They really serve two different purposes.

If you want to just spin around or do a lighter workout, rollers fit that task. Also you can do longer intervals on rollers since your wattage won't be as high.

If you want to do maximal intervals, definitely the trainer. This is your 30s-5min intervals.

I would start out getting a trainer (look for deals now since the winter is over for most places) since its easier to do group indoor training with a trainer. Then next year look for rollers. If you buy quality equipment, it'll last for a long time (especially rollers) so think of it as a longterm investment in your cycling.

Kreitler rollers with flywheel and Killer Head Wind unit.
More realistic resistance than a trainer and helps with balance and bike handling skills.

Take a look at the E-Motion Rollers. They offer more resistence than most trainers, you can stand and sprint out of the saddle and you can't ride off of them. The down side, they are not cheap, but from what I have heard, they heard they are worth the price of admission.

gsteinb likes them. Good endorsement.

+100

Yeah but that guy's an Ahole.

They're for different functions. The rollers are for working on your pedaling form -- you'll notice pretty quickly how balanced your pedaling is on rollers. The trainer is for working on your muscles/heart/lungs (your "engine").

You can't fall off of a trainer
Trainers are easier to pack and store
Rollers Rock!

Trainers are for training. You can do any kind of workout on a trainer.

Rollers are more interesting and more fun, in my opinion, since you feel more like you're on the road. Rollers help to develop a very smooth and powerful stroke, which is a very important skill. But, out of the saddle, all-out sprints on rollers are a great way to injure yourself or your bike.

Get the combo that SushiJoe recommended. You're work your engine just fine. The only thing you can't do is a proper sprint, but I guess with the e-motion setup you can do that, too.

The headwind had me crying like a school girl even almost all the way closed; not to mention it makes a terrible racket.

I got a KK "rock and roll", I don't know if it really compares to rollers, but the unit works well for it's intent.