First of all let me clear i am not the best guy in the forum to answer your question,but let me have my say.
1) If you want a career in web development,then i think you should choose either Java/.NET platform and as you already know HTML,FLASH it will give you the initial boost. For web development i guess you also need to learn a pro image editing tool DreamWeaver/Phptoshop. But if you are through in Java only it will land you on a good career,no nothing is required.
2) Also C,C++ are very good languages. If you can code serious programs then you can be easily absorbed in s/w industry. ( device drivers,socket programming etc).
The field and scope of S/W industry is so vast that i can not describe it all. But the punch line is " for starters ,know one language properly and leave no stone untouched in that language" . I hope you got my point.
P.S - If you are intesested to build a career in search engine optimization ask deep,if interested to foray in Linux ask brainiacs in Open Source.