If you want your PS2 to survive, you need some sort of modchip. Without one, you can really FUBAR your box. Your best solution depends on your model version, video format, wallet size, and desired level of complexity. There is currently a thread going on this forum's member's mod of choice that might shed a little light on what's most popular--it seems to be driven more by quality than price, so the posts may be worth a read. You can link to it here:
Basically, a pro install of a soldered chip is the best solution all around. The no solder's can work well under limited circumstances, but the top of the line soldered are best for broader compatability. In the long run, the soldered's can cost less as well because you won't need any kind of boot disc set up for each flavor of game played--PS1 CD, PS2 CD, PS2 DVD up to 4.35GB, PS2 DVD >4.35GB, Homebrew developed CD's (ie DivX player or other Console emulators). Alot can go into determing what mod is best for your needs. Decide your needs first, then search a little on the Messiah 2's, Magic 3.xx's, DMS3's, etc. to reach your decision about chip, then you can find an installer in the Buy/Sell/Trade section.
Good Luck, and welcome to PS2Newz.
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.