There are a number of free resources on the Web for verb conjugation. My first stop is usually Wiktionary at the link http://en.wiktionary.org/wiki/Category:Polish_verbs. There is a list of verbs there by infinitive from A-Z and you can look up the conjugations; just be sure and click on the "show" link to show the conjugation. You can also look up auxiliary verbs, or search for verbs based on whether they are perfective or imperfective. It's not an exhaustive list, though. Just because it is my first stop doesn't necessarily mean it's the best place to go. There are still a lot of verbs that you can't find there, but it is growing surprisingly quickly.
Next I go to bab.la at http://pl.bab.la/koniugacja/polski/ (or the same site in English at http://en.bab.la/conjugation/polish/), which seems to have a lot more verbs. Once you get past the alphabetical listing, the listing by each letter of the alphabet is characterized only by "page numbers", so you have to make an approximation of what verb will be on which page (this is an improvement over the previous incarnation, which had no alphabetical listing at all, and you had to guess which page the verb you are looking for would be on based on its position in the alphabet and the popularity of its beginning letter). There is also a search box you can use to search for the verb you want to conjugate...one interesting feature about this search box is that you don't have to type the special characters in the word (e.g., you can type "a" instead of "ą", or "c" instead of "ć", at least in the verbs I tried).
Then there is Tasting Poland at http://www.tastingpoland.com/language/verb/verb_forms.html. This site has the added advantage that in many cases you can look up multiple verb forms rather than just the infinitive, and it usually presents the conjugations in pairs with both the perfective and imperfective side by side. You can either search by letter (actually by groups of letters of the alphabet), or if you prefer to search on a page that has only infinitives, you can go to http://www.tastingpoland.com/language/verb/verb_infinitives.html (or this page for the same list with diacritical marks disabled). This site also does an adequate job of linking the imperfective and perfective verb pairs, listing the verb pairs, and listing the conjugations for both members of the verb pair for most (but not all) of the verbs.
There is also a site that has a labyrinthine discussion of many facets of the Polish language and Polish grammar, all in Polish. Its main page for Polish verb conjugation is at http://grzegorj.w.interia.pl/gram/pl/koniug00.html or http://grzegorj.w.interia.pl/gram/en/koniug00.html in English, but you might want to check out its main page also at http://grzegorj.w.interia.pl/gram/index.html (there is a version of the site in English also but it may not be as complete). This is a good site for discovering all the conjugation types and sub-types, and the categorization structure used here seems to be extremely comprehensive.
Another stop is Wikisłownik at http://pl.wiktionary.org/wiki/Kategoria:polskie_czasowniki, which is Wiktionary in Polish. There seem to be a different selection of verbs here, but again, it's not all that complete. And, strangely enough, there seem to be less verbs here than on the English Wiktionary site, but they are not duplicative of the English site, and I have found some verbs on the Polish site that are not on the English one. There are also not a lot of actual conjugation tables for the verbs but there is a lot of useful information for each verb. When there is a conjugation table, it is usually under "odmiana." For some verbs, if there is a conjugation table, you can hit the "pokaz" link to see more of the conjugation, usually beyond just present tense. Or there might be an "aneks" page that shows the type of conjugation it falls under even if it's not for the actual verb you are looking for. Here is the appendix page for Polish Verbs, which has links near the top for all the different conjugation types. Here also is an example of Conjugation I, and you can go to the other conjugations from the links at the bottom of this page.
There is also Verbix, where you can choose from a search box or a list of verbs. The character set seems a little messed up sometimes so you might have to figure out what characters substitute for the wrong ones listed. Also it seems to only list imperfective verbs and the search box won't find perfective verbs. But it does list the perfective verb in the conjugation table.
You can also try Gigadictionary. Simply type the verb you are looking for into the "search" box and most of the time it will come up with a conjugation table if the verb is in their database.
One of these sites listed above will probably have a conjugation for the verb you are looking for. Most of these sites don't do a great job of linking up the verb pairs of imperfective and perfective verbs, in my opinion.
Some other sites are Conjugations of Common Verbs, which only have a few of the most common Polish verbs, Verb In Polish, which once again only has a few sites (and mostly talks about rules of conjugation), and Deklinacje I Koniugacje, which covers some rules of both noun declension and verb conjugation. Also there is Parts Of Speech: Verbs, which has some minor discussions about verb conjugation. These are not comprehensive sites, but might provide some minor clarifications. Remember also that you can open any Polish sites (or sites in just about any foreign language) in Google Chrome and it will offer a translation for you.
You might also want to check my blog post on Polish Noun Declension for information on declining nouns, as well as adjectives and pronouns.