ok, so with strobes (i.e. not continous lights), there are two basic choices - speedlights (hotshoe flashes) or monolights/monoblocs (studio flashes). for studio, monolights are standard since they are much more powerful for the same amount of money, and they have modeling lights so you can more easily visualize the shadows before making an exposure.
whatever light you buy, it can be modified...and it has to be, if you want a soft, diffuse light. the typical way to soften light is with an umbrella or softbox. umbrellas are cheaper, but they "spill" much more light to either side, giving you less control if you only want to light a specific area or subject, and the catchlights are much less attractive. the problem is softboxes are a lot more expensive.
finally, you have to consider the brand. the major brands (Profoto, Elinchrom, Alienbee...a couple others) have readily available modifiers of multiple sizes, and the light quality and consistency (particularly the consistency) is better. there're some other advantages too, but I think you can forget about that for now.... and of course, they cost a lot more. Adorama has their Flashpoint series, and I think B&H has Impact, which are great for the cost, but the choice of modifiers are much more limited. an exception is Calumet Genesis lights - they have the Elinchrom mount, so if you decide you want to get expensive lights, you can keep your modifiers and just upgrade the monolight. it's up to you if you want the flexible or the inexpensive choice.
I guess I should mention Alienbees are still considered an inexpensive choice (just a well-supported one) and that you can only buy them if you're in the US or Canada.
other miscellaneous things: you should buy a flash meter. it takes the guessing out of ratios. for light stands, make sure you get heavy duty ones for your monolights. try to get one at least 10' tall. if you get pretty serious about your light, whatever room you end up using as your studio should eventually be painted neutral gray.
more reading here:
http://strobist.blogspot.com/
and here are some links:
http://photography-on-the.net/forum/showthread.php?t=138912
the first site is aimed for speedlights and portable lighting, but you can skip to the parts about modifiers, quality of light, etc.
if you'd like a book, I can recommend Master Lighting Guide for Portrait Photographers, by Christopher Grey.
edit: I forgot to mention triggers. you can do this using a PC sync cord, I think...but I don't think a T1i has an PC input so either you go wireless or get a hotshoe-PC adapter. for wireless, you can trigger monolights optically with a flash, or you can use radio triggers.